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PHYSIOLOGICAL  AGE  AND 
SCHOOL  ENTRANCE 


BY 

ARTHUR  K.  BEIK 

Clark  University 


A  DISSERTATION  SUBMITTED  TO  THE  FACULTY  OF 
CLARK  UNIVERSITY,  WORCESTER,  MASS.,  IN  PARTIAL 
FULFILLMENT  OF  THE  REQUIREMENTS  FOR  THE 
DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  AND  ACCEPTED 
HE  RECOMMENDATION  OF  WILLIAM  H.  BURNHAM 


Reprinted  from  the  PEDAGOGICAL  SEMINARY 
September,   1913,  Vol.  XX,  pp.  2/7-321 


PHYSIOLOGICAL  AGE  AND 
SCHOOL  ENTRANCE 


BY 

ARTHUR  K.  BEIK 

Clark  University 


A  DISSERTATION  SUBMITTED  TO  THE  FACULTY  OF 
CLARK  UNIVERSITY,  WORCESTER,  MASS.,  IN  PARTIAL 
FULFILLMENT  OF  THE  REQUIREMENTS  FOR  THE 
DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  AND  ACCEPTED 
ON  THE  RECOMMENDATION  OF  WILLIAM  H.  BURNHAM 


Reprinted  from  the  PEDAGOGICAL  SEMINARY 
September,  1913,  Vol.  XX,  pp.  277-321 


H4 


PHYSIOLOGICAL  AGE  AND  SCHOOL  ENTRANCE1 


By  ARTHUR  K  BEIK,  Clark  University 


INTRODUCTION 

Child  study  has  recognized  in  a  general  way  alternating, 
or  at  least  differentiated,  periods  of  development,  roughly 
classified  according  to  predominant  characteristics,  physical 
and  mental,  and  located  with  reference  to  the  age  of  the 
child  in  years.  Infancy  is  the  term  usually  applied  to  the 
first  year  or  years  of  life.  Following  infancy  there  comes 
the  period  of  childhood,  pretty  sharply  marked  off  at  the 
later  limit  by  the  characteristics  accompanying  the  attainment 
of  pubescence. 

The  period  of  childhood  is  again  variously  divided  by  the 
different  authors,  the  location  of  the  division  points  depend- 
ing upon  the  characteristics  chosen  as  division  marks.  Be- 
cause of  the  grouping  of  some  important  factors  about  those 
years  at  which  school  is  usually  begun,  it  is  becoming  more 
general  to  designate  this  as  a  natural  division  point,  or  per- 
haps better,  nodal  period,  of  development.  The  time  preced- 
ing this  nodal  period  is  referred  to  as  "  earlier  childhood/' 
while  the  time  from  this  to  the  appearance  of  pubescence  is 
referred  to>  as  "  later  childhood."  Later  childhood,  then,  be- 

1  Pres.  G.  Stanley  Hall  suggested  the  field  in  which  to  work  out 
this  thesis.  The  suggestions,  advice  and  helpful  criticism  received 
from  Dr.  W.  H.  Burnham  made  its  completion  possible.  For  the 
helpful  assistance  from  both  these  persons  the  writer  wishes  to 
acknowledge  his  indebtedness.  He  wishes  also  to  express  his  thanks 
to  those  who  assisted  in  the  collection  of  material,  among  whom 
should  be  mentioned  especially  Dr.  Theodate  L.  Smith  and  the  library 
staff. 


274491 


28O  PHYSIOLOGICAL   AGE    AND    SCHOOL    ENTRANCE 

Finally,  this  stage  of  development  is  reached  by  girls  earlier 
than  by  boys,  as  has  been  indicated  by  almost  every  study  of 
development  having  to  do  with  this  period  of  life. 

While  the  close  of  later  childhood  is  thus  pretty  clearly 
marked  off  by  prominent  developmental  features,  there  is  not 
at  its  beginning  such  a  clear  cut  and  astounding  transition. 
Those  factors  which  may  be  used  as  marks  of  development 
are  much  harder  to  distinguish,  and  therefore  to  correlate. 
There  is  available,  however,  a  considerable  body  of  facts  that 
may  assist  us  in  the  solution  of  one  or  two  of  the  most  im- 
portant problems  that  have  to  do  with  this  period,  and  in  the 
statement  of  some  other  problems  that  need  solution. 

Among  the  important  problems  are  these  two:  (i)  Is 
there,  at  the  age  of  five  or  six  or  seven  years,  evidence  of  a 
transition  or  nodality  of  development  comparable  in  any  man- 
ner to  the  transitional  stage  at  puberty?  (2)  Is  the  advance- 
ment in  the  two  sexes  equal  at  this  period  of  life,  and  if  not, 
how  do  they  differ  ?  We  shall  take  these  up  in  order. 

EVIDENCES  OF  NODALITY 

The  School  Age. — Turning  to  the  first  of  the  problems  just 
indicated,  it  may  be  worth  while,  before  taking  up  the  dis- 
cussion of  actual  physical  characteristics,  to  point  out  that 
this  period  of  the  child's  life  has  for  centuries  been  recog- 
nized in  a  practical  way  as  transitional,  in  that  it  represented 
the  time  for  the  beginning  of  formal  education.  The  actual 
chronological  age  differed  somewhat  with  different  peoples, 
but  for  the  most  part  formal  training,  as  distinguished  from 
home  training  was  begun  at  the  age  of  six  or  seven  years. 

Of  China,  Douglass  wrote  (31,  p.  165)  :  "  School  life 
commonly  begins  at  the  age  of  six,  and  the  youthful  learner 
is  at  once  set  to  learn  by  heart  easy  text-books  which  give  in 
short  sentences  the  leading  principles  of  Chinese  polity." 
Monroe  states  that  in  the  old  Greek  period  the  Spartan  boy 
was  taken  after  seven  years  of  training  under  the  direct  care 
of  the  mother  and  put  under  charge  of  assistants  to  the  paeda- 
monus,  being  cared  for  from  that  time  on  in  public  barracks  at 
public  expense  (56,  p.  74).  Similarly,  Athenian  boys  began 
attendance  at  school  at  about  the  age  of  seven  years  (56,  pp. 
82-3).  Plato,  in  his  ideal  Republic  would  have  the  boys  taught 
music  and  gymnastics  from  the  age  of  seven  on  (56,  p.  135). 
Medieval  and  modern  education  have  fallen  into  line.  The 
legal  age  for  school  entrance  in  most  states,  and  in  most 
countries  also,  at  the  present  time,  falls  within  the  sixth  or 
seventh  year.  Thus  in  the  educational  practice  of  most  nations 
it  has  been  found  experimentally  that  at  about  this  time  of 


PHYSIOLOGICAL    AGE   AND    SCHOOL    ENTRANCE  28l 

life  the  child  has  reached  such  a  stage  of  development  that  he 
can  undertake  the  tasks  involved  in  education  of  a  formal 
nature. 

If,  now,  we  turn  attention  to  the  more  tangible  evidences  of 
the  stage  of  development,  we  are  led  to  several  considerations. 
There  are  the  matters  of  growth,  both  in  height  and  weight, 
dentition,  growth  of  various  parts  of  the  body,  including 
skull,  brain,  larynx,  eye,  etc.  Another  group  of  facts  also, 
related  both  to  neurological  structure  and  to  psychology  may 
be  added.  These  have  to  do  with  the  neuro-muscular  control 
of  the  child.  Finally,  a  few  suggestions  may  be  obtained  from 
the  field  of  pathology. 

Height  and  Weight. — As  regards  growth  in  height  and 
weight,  it  is  generally  agreed  that  the  closing  years  of  the  later 
childhood  period  are  years  of  retarded  growth.  This  con- 
clusion is  based  upon  the  results  of  numerous  extended  inves- 
tigations. Conclusions  regarding  the  earlier  years  of  the 
period  are  much  less  definite,  partly  because  of  insufficient 
data,  partly  because  of  a  difficulty  in  interpreting  the  mean- 
ing of  the  growth  curves  for  these  years. 

Burk,  who  summarized  the  available  statistics  up  to  the 
time  of  his  study,  1898,  writes  as  follows  (17,  p.  257)  : 

"  If  now  we  turn  to  Table  A  of  heights,  taking,  for  example,  the 
larger  American  studies  of  Bowditch,  Peckham  and  Porter,  we  see  that 
the  rate  of  growth  is  somewhat  rapid  in  the  beginning,  the  sixth  or 
seventh  year,  and  decreases  with  fluctuations  until  about  ten  years  in 
girls  and  twelve  years  in  boys,  when1  the  prepubertal  acceleration  sets 
in.  This  general  decrease  is  to  be  noticed  in  all  the  larger  studies, 
though  the  year  of  the  beginning  of  prepubertal  increase  varies  a  year 
or  so.  The  same  decrease  in  rate  from  six  years  up  to  the  time  of  the 
prepubertal  increase  is  to  be  observed  similarly  in  the  case  of  girls. 
Curves  constructed  from  absolute  annual  increases  show,  as  a  rule,  in 
this  childhood'  period  one  or  two  pronounced  fluctuations,  but  they  do 
not  occur  with  a  regularity  in  all  charts  sufficient  to  be  of  assurance 
that  their  cause  is  certainly  physiological  and  not  merely  statistical. 
Nevertheless,  it  will  be  observed  that  the  curves  are  by  no  means 
regular.  .  .  ." 

Although  pointing  out  thus  clearly  the  irregularities  in  the 
curve  for  these  early  years,  Burk  goes  on  to  conclude  that,  in 
the  absence  of  determinative  data,  it  is  perhaps  better  to  re- 
gard the  period  from  about  six  years  on  as  one  of  a  general 
decrease  in  growth  rate,  with  one  or  two  minor  fluctuations. 
The  investigations  of  Combe,  Landsperger  and  Carstadt,  made 
upon  a  comparatively  small  number  of  children,  but  more 
upon  an  individual  plan,  are  pointed  to  as  justifying  this 
view  (17,  p.  258). 

Smedley,  in  the  Chicago  investigations,  noticed  something 


282  PHYSIOLOGICAL   AGE   AND   SCHOOL   ENTRANCE 

of  these  irregularities  in  the  early  school  years.  Following 
his  reference  to  the  pubescent  acceleration  of  growth,  he 
writes  (84,  p.  32)  :  "  The  charts  seem  to  show  that  a  similar 
but  less  well  marked  period  of  activity  is  present  from  the 
beginning  of  school  life  to  the  age  of  nine." 

Englesperger  and  Ziegler  (32,  Bd.  i)  found  that  of  the 
children  in  the  first  year  of  school,  those  between  the  ages  five 
years  and  nine  months  and  six  years  were  noticeably  smaller, 
on  the  average,  than  those  from  si'x  years  and  one  month  to 
seven  years  of  age.  The  averages  for  these  periods  were : 

Boys  Girls 

5  yr.  9  mo. — 6  yr.=  109-65  cm.  106.25  cm. 

6  yr.  i  mo. — 7  yr.=  m.66  cm.  110.77  crn- 

They  found  considerable  differences  in  height  at  this  period 
between  half  year,  and  even  fourth  year  groups. 

A  tabulation  comparing  the  weights  of  these  periods  showed 
that  a  smaller  percentage  of  those  under  six  years  had  gained 
than  of  those  over  six  years  of  age.  This  was  on  the  com- 
parison of  weights  eight  weeks  apart  at  the  beginning  of 
school. 

Stratz  (86,  p.  66),  in  Germany,  on  the  basis  of  rather 
limited  statistics,  agrees  with  a  former  author,  Bartel,  in 
making  the  first  four  years  a  period  of  bodily  "  fullness,"  the 
years  from  five  to  seven,  inclusive,  a  period  of  "  stretching," 
or  spurt  of  growth,  and  the  years  eight  to  ten  a  second  period 
of  bodily  fullness,  preceding  a  second  spurt  from  the  age  of 
eleven  to  fifteen. 

So  far  as  available  statistical  material  is  concerned,  growth 
in  weight  presents  a  condition  similar  to  growth  in  height. 
Without  giving  the  data  these  tabulations  may  be  character- 
ized briefly,  and  their  indications  may  be  stated.  Most  tabu- 
lations begin  with  the  school  age  and  continue  from  that 
time  on,  thus  preventing  comparisons  with  the  years  that 
precede.  Usually,  also,  the  number  of  data  for  the  earliest 
school  years  are  few  in  number.  Again,  statistics  for  weight 
present  an  added  difficulty  in  interpretation  because  of  the 
greater  variability  in  this  factor.  So  far  as  comparisons  of 
absolute  figures  may  be  relied  upon,  there  is  only  a  continuous 
but  variable  increase  in  weight  from  year  to  year  in  the  two 
sexes,  up  to  the  age  of  nine  or  ten,  when  a  retardation  occurs. 
Boys  appear  to  be  slightly  superior,  throughout  the  entire 
course. 

There  is  slight  suggestion  of  a  spurt  of  growth  in  the  be- 
ginning school  years,  but  there  is  not  sufficient  evidence  to 
establish  the  point.  What  is  needed  here  is  a  collection  of 


PHYSIOLOGICAL    AGE   AND   SCHOOL    ENTRANCE  283 

more  data,  beginning  with  the  lower  years  and  continuing 
through  the  beginning  school  years.  One  cannot  see  in  these 
studies  of  height  and  weight  a  definite  proof  of  a  character- 
istic of  growth  at  this  period.  It  is  a  fact,  however,  that 
from  the  larger  investigations  the  results  strongly  suggest  a 
slight  acceleration.  It  is  also  to  be  remembered  that  most  of 
the  tabulations  have  paid  attention  to  yearly  age  gro-ups  only. 
Much  more  accurate  would  be  a  comparison  of  age  groups 
for  fourth  years  or  perhaps  for  months. 

The  rather  indefinite  studies  of  development,  as  indicated 
by  increase  in  growth  in  height  and  weight,  may  be  supple- 
mented by  some  more  definite  facts  with  regard  to  individual 
organs  or  parts  of  the  body  that  give-  more  distinct  evidence 
of  a  nodality  at  the  school  age. 

Development  of  Teeth  and  Jaws. — The  period  with  which 
we  are  here  dealing  is  distinctly  a  transitional  one  as  regards 
the  development  of  the  teeth  and  jaws.  These  present  a  num- 
ber of  phenomena,  transitional  as  well  as  developmental  in 
their  nature,  that  group  themselves  about  the  years  in  which 
the  change  from  first  to  second  dentition  occurs.  Some  of 
these  are  very  evident,  others  less  so,  but  altogether  they  make 
up  such  a  group  of  developmental  processes,  so  closely  asso- 
ciated with  each  other,  and  also  to  other  phases  of  physical 
and  mental  development  that  they  deserve  to  be  noted  con- 
siderably in  detail. 

Aside  from  this,  there  are  also  other  well  grounded  reasons 
for  dwelling  somewhat  at  length  upon  this  topic.  I.  Anatom- 
ically, the  teeth  and  jaws  are  the  most  important  structures 
in  the  facial  part  of  the  skull.  Much  of  the  remaining  por- 
tion is  of  rather  secondary  nature,  its  purpose  being  to  fur- 
nish place  for  attachment  of  muscles  or  to  give  proper  bracing 
and  support  for  these  parts.  2.  On  the  side  of  physiological 
functioning  the  teeth  and  jaws  are  extremely  important. 
Upon  them  devolves  a  great  part  of  the  preparation  of  food 
in  the  process  of  digestion,  not  to  mention  the  part  they  play 
in  articulate  speech.  3.  Again,  from  the  view  point  of  hygiene, 
it  may  be  said  that  columns  of  good,  sound  teeth,  so  located 
as  to  bring  their  chewing  surfaces  into  proper  occlusion,  are 
requisites  of  good  health.  The  absence  of  these  conditions 
may  lead  to  any  of  a  number  of  allied  disturbances,  to  which 
more  detailed  reference  will  be  made  later.  4.  Finally,  since 
they  occupy  so  prominent  a  place  anatomically,  the  form  and 
general  outline  of  the  face  are  to  a  great  extent  dependent 
upon  teeth  and  jaws.  It  therefore  follows  that  from  the  view 
point  of  esthetics  the  proper  formation  and  development  of 
teeth  and  jaws  may  not  be  left  unconsidered.  Thus  we  may 


284  PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE 

say  that  from  any  of  the  four  view  points,  esthetic,  hygienic, 
functional  or  structural,  development  of  teeth  and  jaws  de- 
serves the  fullest  consideration.  We  shall^  attempt  to  con- 
sider the  topic  from  all  four  of  these  view  points  in  the  follow- 
ing paragraphs  devoted  to  it. 

While  most  concerned  with  the  transitional  phenomena, 
so  much  depends  upon  preceding  and  following  developmental 
processes  that  a  rapid  review  of  the  entire  period  of  dentition 
may  be  of  value  in  setting  forth  more  clearly  the  character- 
istics of  the  transitional  period.  In  this  review,  it  is  assumed 
that  the  reader's  general  knowledge  of  form,  names,  and  com- 
position of  the  teeth  is  sufficient  to  render  detailed  descrip- 
tions unnecessary.  Since  similar  knowledge  with  regard  to 
the  jaws,  on  the  other  hand,  seems  to  be  less  general,  descrip- 
tions of  the  principal  structures  with  which  we  shall  need  to 
deal  will  be  included.  For  the  sake  of  clearness,  the  facts 
with  regard  to  development  of  the  teeth  will  be  presented  first, 
then  those  with  regard  to  development  of  the  jaws.  With 
these  two  groups  of  facts  before  us,  we  may  next  proceed  to 
discuss  their  relationship  and  its  significance,  and  arrive  at 
some  conclusions.  With  these  hints  as  to  method  of  proced- 
ure before  us,  we  turn  next  to  the  presentation  of  the  facts. 

Although  the  eruption  of  the  first  or  temporary  teeth  from 
the  gums  does  not  take  place  until  some  time  after  birth,  the 
formation  of  their  crowns  begins  very  early  in  the  developing 
embryonic  jaw.  Their  calcification  is  already  far  advanced 
at  the  time  of  birth.  The  early  formation  and  development 
of  these  is  somewhat  as  follows :  Above  the  gums,  along  the 
rudimentary  jaw  of  the  embryo,  there  is  formed  very  early 
a  ridge  of  epithelial  cells.  At  each  of  the  ten  points  at  which 
a  tooth  crown  is  to  be  formed,  a  depression  or  invagination 
occurs  in  this  ridge,  pushing  on  downward  into  the  jaw  in 
a  line,  as  it  were,  or  tube,  and  expanding  at  the  end  into  a 
bell-shaped  structure, — the  enamel  organ.  Gradually  the 
enamel  organ  grows  down  over  the  top  and  sides  of  a  small 
mound-like  enlargement  that  rises  up  from  the  deeper  tissue, 
— the  dental  germ.  Again  a  little  later  the  connection  of  the 
enamel  organ  with  the  epithelial  ridge  above  is  lost,  enamel 
organ  and  dental  germ  together  become  isolated  from  the 
surrounding  parts  and  enclosed  in  a  "  dental  sac,"  and  within 
this  sac  the  two  organs  proceed  to  build  up  the  parts  of  the 
tooth  crown.  Out  of  the  soft  cells  that  make  up  the  enamel 
organ  is  formed  the  enamel ;  out  of  those  of  the  tooth  germ 
is  formed  the  dentine  or  ivory  of  which  the  inner  part  of  the 
tooth  is  composed,  and  within  which,  again,  is  the  open  cavity 
containing  the  pulp. 


PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE  285 

The  transformation  of  these  soft  cells  into  the  hard  struc- 
tures of  the  crown  is  accomplished  by  means  of  the  deposition 
of  lime  salts  within  the  cells  themselves,  and  is  usually  spoken 
of  as  a  process  of  calcination  or  calcification.  The  processes 
are  not  the  same  in  both  cases,  however.  While  the  cells  of 
the  enamel  organ  become  changed  into  solid  crystals,  those 
of  the  dental  germ  receive  the  lime  deposits  only  around  the 
outside  in  such  a  way  that  the  resulting  structures  are  elongate 
tubes.  The  central,  uncalcified  portions  remain  as  fine  fibrils 
which  are  connected  with  the  soft  pulp  of  blood-vessels  and 
nerves  that  fill  the  inner  cavity  of  the  tooth.  The  dentine 
tubes  thus  formed  are  of  considerable  length  and  extend  out- 
ward radially  from  the  pulp  cavity  to  the  enamel  "  roof  "  of 
the  tooth. 

The  direction  in  which  the  calcification  proceeds  differs  in 
the  two  organs.  It  will  be  remembered  that  the  enamel  organ 
folds  over  and  encloses  the  dental  germ.  Now,  the  calcifica- 
tion begins  at  the  contiguous  surfaces  of  the  two  organs  and 
proceeds  in  both  directions.  For  the  enamel  cells,  then,  cal- 
cification proceeds  from  the  inner  surface  toward  the  outer; 
for  the  dentine  cells,  it  proceeds  from  the  outer  surface  in- 
ward toward  the  pulp  cavity. 

Enamel  and  dentine  differ  also  in  another  way.  The  enamel 
crystals  receive  no  more  nourishment  after  being  once  formed. 
The  dentine  cells,  on  the  other  hand,  continue  to  receive  some 
nourishment  throughout  the  life  of  the  tooth  by  means  of 
the  soft  fibrils  in  the  central  tubular  portions.  (63.  p.  31.) 

As  the  development  of  a  crown  proceeds  beneath  the  gums 
there  is  deposited  around  it  a  layer  of  bony  substance,  so 
that  by  the  time  it  is  completed  it  is  almost  enclosed  in  a 
bony  case  or  crypt.  The  top  of  the  crypt  is  open,  though 
the  aperture  is  not  large  enough  for  the  crown  to  pass 
through  without  absorption  of  some  of  the  tissue  from  its 
edges.  This  is  what  occurs  at  the  time  of  eruption  of  the 
crown. 

After  the  manner  thus  described  there  are  formed  ten  tooth 
crowns  in  each  of  the  jaws.  Their  calcification  is  not  entirely 
completed  by  the  time  of  birth,  but  it  is  completed  within 
the  first  few  months  of  life.  Then  they  emerge  from  the 
gums  to  form  the  "  temporary  set  "  that  functions  during  the 
early  years  of  the  child's  life.  Of  these,  the  incisors  and 
canines  are  small,  as  compared  with  the  corresponding  teeth 
that  follow.  The  bicuspids,  or  milk  molars,  on  the  other  hand, 
are  larger  than  the  permanent  bicuspids  that  follow.  In  this 
way  ample  provision  is  made  for  the  mastication  of  such 


286  PHYSIOLOGICAL   AGE   AND   SCHOOL   ENTRANCE 

foods  as  the  child  is  able  to  digest  and  assimilate  during  his 
early  years. 

Some  weeks  after  birth  the  crowns  of  the  temporary  set 
are  completed  and  begin  to  erupt  from  the  gums.  The  first 
become  visible  at  about  the  sixth  to  eighth  month  of  life, 
usually,  and  at  the  age  of  about  two  and  one-half  to  three 
years  the  child  is  equipped  with  a  full  set  of  twenty.  Ap- 
pearance is  usually  in  groups,  beginning  with  the  central  in- 
cisors and  proceeding,  in  a  general  way,  backward  from  these, 
with  intervals  of  time  elapsing  between  the  several  groups. 
Witzel  reports  the  usual  time  for  the  eruption  of  these,  as 
given  by  Thomas  and  Baume,  to  be  as  follows  (98,  p.  — )  : 

Central  incisors  6-  8  mo. 

Lateral  incisors   6-12  mo. 

Anterior  bicuspids 12-16  mo. 

Canines   15-20  mo. 

Posterior  bicuspids   20-30  mo. 

The  basis  for  this  statement  is  not  given,  no  mention  being 
made  of  actual  investigation.  The  periods  given  are  those 
within  which  the  eruption  from  the  gums  usually  occurs.  It 
is  possible  for  the  teeth  to  appear  much  later,  however,  and 
yet  be  normal.  It  is  also  possible  for  a  few  of  the  crowns 
to  be  already  visible  at  birth  and  the  teeth  be  normal,  though 
this  is  very  often  the  result  of  diseased  conditions. 

The  process  by  which  a  tooth  crown  erupts  is  somewhat 
complex.  The  edges  of  the  opening  in  the  bony  crypt  must 
first  be  reabsorbed,  making  room  for  the  crown  to  push 
through.  The  gums  that  form  the  covering  are  next  absorbed. 
While  this  is  going  on  and  the  crown  gradually  pushing  up- 
ward, additions  are  made  to  the  root  from  cells  at  the  base 
of  the  crown,  and,  once  the  final  position  is  attained,  the 
root  becomes  fastened  into  place  by  the  bony  tissue  built  up 
around  it.  The  root  canal  remains  as  a  rather  wide  opening 
for  some  time,  however,  the  dentine  being  built  up  gradually 
until  the  root  is  solid,  except  for  the  narrow  canal  through 
which  the  vessels  and  nerves  are  admitted  to  the  pulp  cavity. 

The  tissue  built  up  around  the  teeth  and  within  which  their 
sockets  are  found  is  known  as  the  alveolar  border  of  the 
jaw  or  alveolar  process.  It  is  developed  with  the  teeth  and 
apparently  for  the  specific  purpose  of  holding  them  in  posi- 
tion. Fuller  description  of  it  may  be  reserved  until  later. 
A  description  of  the  means  by  which  the  tooth  roots  are 
firmly  fastened  within  it,  however,  is  in  place  at  this  point. 
This  can  best  be  given  in  the  words  of  Dr.  Angle,  taken 
from  his  paragraph  on  "  Peridental  Membrane"  (i,  p.  122). 


PHYSIOLOGICAL   AGE  AND   SCHOOL    ENTRANCE  287 

"  The  peridental  membrane  is  a  strong,  fibrous  membrane  forming  a 
close,  cushion-like  investment  of  the  roots  of  the  teeth,  and  is  the 
medium  of  attachment  between  the  alveolar  process  and  the  cementum. 
It  is  composed  largely  of  inelastic  connective  tissue,  and  is  richly 
supplied  with  nutrient  vessels,  nerves,  cells,  and  glands.  Its  function 
is  three-fold: 

"  First,  vital,  for  the  formation  of  the  alveolar  process  on  one  side 
and  the  cementum  on  the  other. 

"  Second,  sensory,  through  which  the  most  delicate  touch  of  the 
tooth  is  felt. 

"  Third,  physical,  holding  the  tooth  in  position  in  the  alveolar  socket, 
and  resisting  the  movements  of  the  teeth  in  the  various  directions.  It 
also  supports  the  soft  tissues  about  the  teeth." 

Continuing,  Dr.  Angle  enumerates  the  kinds  of  cells  of 
which  the  peridental  membrane  is  composed  as,  I,  fibroblasts, 
for  the  formation  of  fibers  of  the  membrane;  2,  osteoblasts, 
for  the  formation  of  the  alveolar  process;  3,  cementoblasts, 
for  forming  the  cementum;  4,  osteoclasts,  for  disintegrating 
calcified  tissue;  and  finally,  5,  glands,  the  function  of  which 
is  as  yet  imperfectly  understood  (i,  p.  123). 

Malposition  of  temporary  teeth  is  rare.  When  it  does  occur, 
it  is  easily  corrected,  under  normal  conditions,  by  means  of 
the  pressure  from  lips  and  tongue.  But  while  this  is  true, 
abnormal  conditions  may  as  readily  cause  the  teeth  to  be 
moved  from  their  proper  positions  and  thus  bring  about  a 
malocclusion. 

But  the  temporary  crowns  are  not  formed  alone  in  the 
embryonic  jaw.  The  beginnings  of  the  permanent  crowns  are 
also  present  at  a  very  early  stage.  Very  early  in  the  develop- 
ment of  the  enamel  organ  of  each  of  the  temporary  teeth  a 
second  line  or  tube  of  epithelial  cells  pushes  down  by  its 
lingual  side.  It  appears  as  a  branch  of  the  tube  which  de- 
velops into  the  enamel  organ  of  the  temporary  tooth.  In 
structure,  too,  it  is  similar,  and  its  development,  later,  after 
the  manner  described  for  the  temporary  tooth,  results  in 
the  formation  of  the  crown  of  the  permanent  tooth. 

Aside  from  the  ten  corresponding  to  the  crowns  of  the 
temporary  set,  there  are  also  six  other  germs  in  each  jaw, 
as  the  beginnings  of  the  molars  of  the  second  set.  The  child 
at  birth,  then,  has  in  each  jaw  the  almost  completed  crowns 
of  the  ten  temporary  teeth  and  also  the  germs  of  the  sixteen 
permanent  teeth  at  various  stages  of  development.  The  com- 
pletion of  the  permanent  crowns  is  of  course  later  than  that 
of  the  temporary,  their  time  of  most  rapid  growth,  according 
to  Pedley  (62)  being  from  birth  to  three  or  four  years  of 
age.  Johnson  places  the  critical  period  for  their  calcification 
at  from  birth  to  the  age  of  five  years,  that  of  the  first  perma- 
nent molars  having  been  begun  even  before  the  birth  of  the 
child  (51). 


288  PHYSIOLOGICAL   AGE   AND    SCHOOL    ENTRANCE 

The  time  of  these  processes  is  given  more  in  detail  by 
Witzel  (98,  p.  17)  : 

"  The  calcification  of  the  crowns  of  the  incisive  teeth  begins  between 
the  first  and  second  year  and  the  calcification  of  the  canine  tooth  in 
the  third  year.  In  the  fifth  year  of  age  the  tuberosities  for  the  second 
molar  tooth  are  developed  and  in  the  ninth  those  for  the  third.  About 
the  time  of  the  ninth  year  no  remarkable  processes  of  calcification  take 
place  in  the  crowns,  except  in  the  wisdom  tooth,  but  the  roots  are  not 
everywhere  fully  developed. 

The  ages  mentioned  are  of  course  only  approximate,  and 
vary  within  wide  limits. 

From  this  it  follows  that  from  birth  to  about  five  years  of 
age  is  a  critical  period  for  all  the  permanent  set,  except  the 
wisdom  teeth.  During  this  period  the  dental  germs,  many 
of  which  have  begun  development  at  the  time  of  birth,  attain 
their  final  form,  make  their  most  rapid  growth  and  undergo 
a  great  part  of  the  process  of  calcification.  In  this  connection 
it  should  be  emphasized  that  when  once  formed  and  com- 
pletely calcified,  these  crowns  are  adult  crowns,  as  large  as 
they  will  ever  be,  and  subject  to  neither  growth  nor  repair, 
so  far  as  the  organism  to  which  they  belong  is  concerned. 
Completion  of  the  crowns  is  accompanied  by  enlargement  of 
the  alveolar  border  and  growth  in  some  parts  of  the  jaw, 
with  considerable  redistribution  of  the  inner  structures. 

Thus  far  we  have  noted  the  principal  features  in  the  forma- 
tion and  calcification  of  the  temporary  crowns,  marked  the 
important  changes  involved  in  their  eruption  and  in  their 
fixation  into  position  by  means  of  developing  root  structures 
and  alveoli,  and  have  traced  the  important  steps  in  the  process 
by  which  the  permanent  crowns  are  formed,  developed  and 
calcified  within  the  alveolar  portions  of  the  jaws.  Each  one 
of  these  is  a  developmental  feature  characteristic  of  the  earlier 
years,  and  constitutes  a  step  in  the  preparation  for  the  coming 
of  the  permanent  teeth.  The  time  immediately  preceding  sec- 
ond dentition  is  therefore  a  remarkable  one  for  the  child, 
considered  from  the  view  point  of  his  dentition.  Within  his 
jaws  there  are  i,  a  full  set  of  twenty  functioning  temporary 
teeth,  2,  the  practically  completed  crowns  of  their  twenty  suc- 
cessors, many  of  which  are  larger,  3,  the  completed  crowns 
of  the  four  first  permanent  molars  and  practically  completed 
crowns  of  the  four  second  molars,  and  4,  the  only  partially 
developed  germs  of  four  wisdom  teeth  or  third  molars.  This 
is  the  normal  condition  of  the  child's  jaws  at  the  age  of  five 
or  six  years.  Transition  to  the  second  dentition  usually  begins 
very  soon  afterward. 

In  discussing  the  eruption  of  the  permanent  crowns  we  may 


PHYSIOLOGICAL    AGE   AND   SCHOOL    ENTRANCE 


289 


first  give  attention  to  the  time  of  their  appearance,  and  then 
turn  to  the  description  of  the  process  by  which  it  is  brought 
about. 

Time  of  appearance  of  the  permanent  teeth  has  been  made 
the  object  of  a  number  of  investigations.  Some  of  these  are 
of  no  value  for  our  purpose,  since  they  do  not  differentiate 
the  sexes.  Of  the  three  available  that  do,  one  is  not  extended, 
but  the  other  two  are  sufficiently  so  to  make  their  results 
valuable. 

First  let  us  turn  to  the  statistics  of  Boas  and  Wissler.  Their 
material  was  a  series  of  plaster  casts  taken  from  the  palates 
of  219  boys  and  276  girls.  They  therefore  contain  data  for 
the  upper  jaw  only.  The  following  Table  A  is  their  table 
numbered  "  XI  C."  giving  results  in  percentages  (n,  p.  34)  : 

TABLE  A. 
PERCENTAGE  OF  CHILDREN  HAVING  PERMANENT  TEETH. 


A  prp 

B 

oys 

G] 

rls 

In. 
Inc. 

Out. 
Inc. 

Can. 

Bic. 

ISt 

Mol. 

2nd 
Mol. 

In. 
Inc. 

Out. 
Inc. 

Can. 

Bic. 

ISt 

Mol. 

2nd 
Mol. 

6 

30 

4 

6c 

78 

Q 

6 

I  c 

87 

2 

7 

40 

6 

3 

3 

83 



79 

28 

2 

41 

92 



8 

81 

26 



19 

IOO 



84 

48 

9 

45 

93 

6 

9 

97 

67 

3° 

7 

IOO 

59 

9 

45 

IOO 

2 

10 

IOO 

63 

33 

66 

3 

94 

82 

14 

73 

8 

ii 

95 

61 

IOO 

9 

96 

96 

73 

83 

20 

12 

IOO 

85 

38 

IOO 

ICO 

86 

IOO 

32 

*3 

91 

68 

88 

88 

68 

14 

IOO 

66 

90 

90 

9° 

IS 

75 

IOO 

IOC 

IOO 

Averages  and  variabilities  were  computed  for  the  time  of 
appearance  of  the  several  teeth  and  found  to  be  as  follows 
(12,  p.  35): 

Boys  Girls 

Inner  incisors    7-5±i-5yr-  7.o±i.6yr. 

Outer  incisors 9. 5  ±2.1  8.9  ±2.1 

Bicuspids 9. 8  ±1.6  9.0  ±2. 8 

Canines n  .2  ±  i  .4  11.3  '  ±  I. o 

Second  molars 13. 2  ±2.0  12. 8  ±1.6 


290 


PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE 


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292 


PHYSIOLOGICAL   AGE   AND    SCHOOL    ENTRANCE 


The  investigation  of  Berten  was  much  more  extended.  He 
collected  data  from  some  3,345  children  in  Germany,  of  ages 
ranging  from  five  and  one-half  to  thirteen  and  one-half  years. 
In  the  accompanying  Table  B  are  presented  the  numbers  of 
teeth  present  for  each  half-year  group  within  these  ages. 
This  table  condenses  the  data  found  in  Berten's  tabulation 
(8,  pp.  278-9).  Boldface  figures  indicate  groups  where  100 
per  cent,  were  found  present. 

A  report  of  an  investigation  much  more  extended  than 
either  of  these  appeared  in  recent  years.  Dr.  Rose  has  tabu- 
lated the  number  of  teeth  found  present  in  the  several  groups 
in  case  of  41,021  children  in  Germany,  Sweden,  Denmark, 
Holland,  Belgium,  Bohemia  and  Switzerland.  His  tabulation 
differentiates  upper  and  lower  teeth,  also  sex  groups,  and 
gives  the  averages  and  variabilities  for  the  several  tooth 
groups. 

Table  C  is  his  "  Table  XIV,"  in  which  the  results  of  the 
investigation  are  summarized  (77,  p.  564)  : 

TABLE  C. 

ERUPTION  TIME  OF  PERMANENT  TEETH  IN  41,021  SCHOOL  CHILDREN 

FROM  GERMANY,  SWEDEN,  DENMARK,  HOLLAND,  BELGIUM, 

BOHEMIA  AND  SWITZERLAND. 


Boys=2i,i39 

Girls=i9,882 

Average 
eruption 
time 

Eruption 
time 
varies 
between 
ages 

Average 
eruption 
time 

Eruption 
time 
varies 
between 
ages 

Yr.  Mo. 

Yr.            Mo. 

UPPER  JAW 

Incisor    I  ... 
Incisor  II  ... 
Canine  
Premolar    I. 
Premolar  II. 
Molar    I.... 
Molar  II.... 

7       8 
8      ii 

12           2 

10        5 
ii        4 
6        7 
12        9 

S-S-ii-S  Yr. 
6.  -(?)        " 
7.5-15.        " 
6.5-14-        " 
6.5-15-        " 
5-  ~  9-5 
9-  -15-        " 

7   5      (  -3      Mo.) 
8  6      (  -5        «   ) 
ii   7      (  -7        "   ) 
io   i      (  -4        "   ) 
ii    i      (  -3        "   ) 
6  6      (  -i        "   ) 

12    5      (  -4        "   ) 

5-5-n.     Yr. 
6.  -(?)        " 

7-  -15-        " 
6.5-14.5     " 
7-  -15-        " 
5-  -io.        " 
9-  -15- 

LOWER  JAW 

Incisor    I  ... 
Incisor  II  ... 
Canine  
Premolar    I. 
Premolar  II. 
Molar    I.... 
Molar  II.... 

6     10 

7     ii 

II            2 

ii        3 

12           0 

6       5 
12        3 

5.  -10.     Yr. 

6.    -12. 

?::&  :: 

7.  -15.    " 

5-  -io.        " 
9-  -15-        " 

67      (  -3     Mo.) 

7   7      (  -4        "   ) 
io  3      (-11        "   ) 
io  8      (  -7        «   ) 

io   7      (  -5        "   ) 
6  3      (  -2        "   ) 
ii   9      (  -6        "   ) 

5.  -ii.     Yr. 

6.    -12. 

7-  -i4-        " 
7-  -14-5 
7-  -i5- 

U|    « 

Avg.   of  the 
total       i  4 
eruptions  . 

9     10.0 

9  5.4    (  -4.6  Mo.) 

PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE  293 

Careful  study  of  these  tabulations  will  show  that  they  are 
in  agreement  as  to  the  essential  points  regarding  the  time  and 
the  order  of  eruption  of  the  permanent  crowns.  Each  one 
confirms  the  prevalent  view  that  transition  to  second  denti- 
tion begins  with  the  eruption  of  the  first  permanent  molars. 
This  is  evident  in  the  tabulation  of  Berten,  and  in  the  averages 
from  the  very  extended  investigation  of  Rose.  Berten  writes 
that  in  only  three  cases  did  he  find  the  transition  to  the  perma- 
nent teeth  beginning  before  the  appearance  of  any  molars 
(8,  p.  271). 

Incidentally  it  should  be  noted  that  the  time  for  the  appear- 
ance of  the  first  molars  is  in  the  seventh  year.  Berten's  table 
indicates  that  practically  all  appear  between  the  age  of  six 
years  and  seven  and  one-half,  while  Rose's  averages  all  fall 
between  the  ages  six  years  and  three  months  and  six  years 
and  seven  months. 

Again,  the  more  extended  investigations  of  Berten  and 
Rose  have  furnished  abundant  evidence  in  confirmation  of  the 
view  that  the  lower  teeth  appear,  on  the  average,  earlier  than 
the  upper,  except,  perhaps,  in  case  of  the  canines  and  bicus- 
pids. In  all  the  investigations  a  considerable  variation  in  the 
time  of  appearance  for  the  several  tooth  groups  is  evident. 
From  this  it  follows  that  dentition  does  not  run  a  parallel 
course  in  all  children.  Variation  in  time  of  appearance  is 
least  in  case  of  the  first  molars  and  grows  progressively 
greater  with  each  succeeding  tooth  group,  up  to  the  bicuspids 
and  canines. 

The  order  in  which  the  permanent  crowns  appear  is  repre- 
sented in  these  data.  According  to  them  it  runs :  first  molars, 
inner  incisors,  outer  incisors,  first  bicuspids,  after  which  the 
order  of  the  remaining  groups  is  somewhat  confused.  Berten 
states  (8,  p.  274)  that  most  often  we  find  these  groups  ap- 
pearing in  such  a  way  that  the  lower  canine  follows  the  first 
bicuspids,  and  is  followed,  in  turn,  by  the  upper  second  bi- 
cuspid ;  then  the  lower  second  bicuspid  appears,  and  the  upper 
canine  brings  up  the  rear. 

Finally,  before  leaving  this  topic,  the  point  of  sex  difference 
in  time  of  eruption  of  the  teeth  should  be  pointed  out.  In 
each  of  the  three  tabulations  it  is  clearly  evident,  beginning 
with  the  first  molars,  at  the  very  beginning-time  of  second 
dentition.  Rose's  results  show  the  girls  to  be  two  months 
earlier  in  eruption  of  lower  first  molars;  one  month  ahead  in 
eruption  of  upper  first  molars,  on  the  average.  The  actual 
difference  of  time  is  not  so  evident  in  Berten's  table  because 
of  the  form  in  which  it  is  presented,  but  comparison  of  the 
numbers  of  the  teeth  present  show  that  the  results  would  be 


294  PHYSIOLOGICAL  AGE   AND   SCHOOL   ENTRANCE 

in  agreement.  Presented  in  the  form  of  curves  showing  the 
percentages  of  teeth  present  in  the  various  groups,  Berten's 
data  show  very  clearly  that  this  is  true. 

The  processes  by  which  the  eruption  of  the  permanent 
teeth  is  accomplished  deserve  some  further  consideration. 
Evidently  the  temporary  structures  must  first  be  disposed  of. 
This  is  the  first  step  in  the  eruption  of  the  permanent  set. 
It  is  accomplished  by  a  sort  of  reverse  process  to  that  by 
which  the  temporary  roots  are  builded  down  and  fixed  within 
the  alveolar  border.  Beginning  at  the  lower  parts,  the  roots 
are  again  reabsorbed,  along  with  the  bony  case  of  their 
sockets,  even  before  the  term  of  functioning  of  the  teeth  is 
completed.  Radiographs  showing  partially  reabsorbed  roots 
present  very  much  the  same  appearance  as  those  showing  par- 
tially developed  ones.  Apparently  the  reabsorption,  or  resorp- 
tion, as  it  is  often  called,  is  incited  by  the  pressure  of  the 
developing  permanent  crowns  below.  At  any  rate,  in  normal 
cases  the  process  is  sufficiently  advanced  by  the  time  the  per- 
manent crowns  are  ready  to  appear  to  allow  the  temporary 
tooth  to  be  readily  removed  with  very  slight  disturbance  and 
very  little  pain. 

Evidently  here  are  processes  in  which  the  different  types 
of  cells  in  the  peridental  membrane  described  above,  especially 
the  osteoclasts,  play  a  very  important  part.  Pedley  and  Har- 
rison (63,  p.  52)  would  credit  the  leucocytes  with  an  impor- 
tant part  in  the  resorption  process  also. 

Aside  from  the  resorption  of  the  temporary  roots  there 
is  also  a  process  of  resorption  of  the  cancellated  tissue  that 
surrounds  the  deeply  embedded  crowns,  allowing  for  their 
passage  upward  toward  the  surface.  In  case  of  the  molars, 
this  includes  the  absorption  of  part  of  the  cortical  bone  along 
the  borders  of  the  jaws  where  there  have  been  no  preceding 
temporary  teeth. 

The  growth  process  by  which  the  crowns  emerge,  making 
additions  to  the  roots  while  so  doing,  is  not  essentially  differ- 
ent from  that  of  the  temporary  ones  already  described.  Build- 
ing up  of  the  roots  seems  to  be  a  somewhat  slower  process 
in  this  case,  and  their  final  cementing  into  place  more  per- 
manent. This  latter  is  rather  an  osseous  change  and  will  be 
mentioned  more  in  detail  later,  but  it  should  be  noted  in  this 
connection  that  the  order  is  always  first  tooth  position,  then 
adjustment  of  foundation.  This  is  true  regardless  of  whether 
the  position  assumed  is  normal  or  abnormal.  The  bony  foun- 
dation builds  to  the  tooth,  whatever  may  be  the  position  it 
assumes. 

Again,  difference  in  size,  especially  of  incisors  and  canines, 


PHYSIOLOGICAL   AGE  AND   SCHOOL    ENTRANCE  2Q5 

is  greater  in  the  upper  than  in  the  lower  jaw,  so  that  read- 
justment of  the  two  columns  of  teeth  to  each  other  becomes 
necessary.  This  is  a  fact  of  considerable  importance  for  the 
normal  occlusion  of  the  teeth  of  the  permanent  set.  Whereas 
the  upper  and  lower  teeth  of  corresponding  names  fit  end  to 
end  in  the  temporary  set,  in  the  permanent,  the  greater  size 
of  the  teeth  in  the  upper  column  cause  a  backward  shift  along 
the  sides.  The  normal  condition  is  therefore  for  each  molar 
and  bicuspid  to  articulate,  not  with  a  single  antagonist  in  the 
other  jaw,  but  with  two  teeth. 

So  much  for  the  phenomena  of  dentition.  The  treatment 
is  inadequate,  but  possibly  sufficient  facts  have  been  presented 
in  this  brief  review  to  indicate  that  the  beginning  of  later 
childhood  is  without  a  doubt  a  transitional  period  as  regards 
the  teeth.  Preceding  this  period  time  and  material  are  both 
devoted  to  the  task  of  providing  temporary  structures  and 
preparing  permanent  crowns ;  with  the  eruption  of  the  first 
molars  at  this  period,  however,  is  ushered  in  a  series  of  re- 
markable changes,  every  one  of  which  is  a  step  in  the  direc- 
tion of  dental  maturity.  Dr.  Port  (65)  stated  the  case  nicely 
when  he  referred  to  this  period  of  life  as  one  at  which,  for  the 
dentist,  the  child  becomes  adult.  The  significance  of  these 
phenomena  becomes  greater  when  they  are  associated  with 
others  closely  allied  to  them,  and,  in  a  way,  depending  upon 
them.  To  some  of  these  we  shall  next  give  attention. 

Paralleling  that  of  the  teeth,  there  must  occur  a  pro- 
gressive development  of  the  bony  arches  of  the  jaws  that 
form  their  foundations.  Structurally,  both  jaws  are  complex, 
and  are  in  very  close  relationship  to  the  other  parts  that 
make  up  the  facial  portion  of  the  skull.  Thus  the  upper  jaw 
forms  the  principal  bone  of  the  face,  taking  part  in  the 
formation  of  the  hard  palate,  the  floor  of  the  orbit  and  the 
floor  and  lateral  wall  of  the  nasal  cavity  (?ia,  p.  50).  Cryer 
states  (27,  p.  31)  that  in  a  surgical  operation  removing 
a  right  or  left  maxilla,  "  the  inferior  turbinate,  portions  of 
the  lachrymal,  the  palatal,  the  malar,  and  the  ethmoid  bones 
will  probably  be  removed  with  it."  The  lower  jaw,  on  the 
other  hand,  has  the  distinction  of  being  the  strongest  and 
thickest  bone  of  the  face.  It  is  made  up  of  the  arched  por- 
tion known  as  the  body,  and  the  two  ascending  portions  called 
the  rami,  each  of  which  has  a  flat,  pointed  projection  at  its 
anterior  edge  for  the  attachment  of  muscles,  and  at  the 
posterior  edge  a  convex  process  which  hinges  with  the  for- 
ward portion  of  the  temporal  bone  and  allows  for  the  move- 
ments of  the  jaw. 

Leaving  aside  for  the  moment  the  details  of  structure,  we 


296  PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE 

may  generalize  with  regard  to  the  arched  portions  of  the 
two  jaws  by  saying  that  in  either  case,  the  essential  features 
are  (i)  a  basal  osseous  arch  composed  of  an  outer  shell 
of  cortical  bone  rilled  in  with  spongy,  cancellated  tissue,  and 
(2)  an  alveolar  border  consisting  of  two  thin,  hard,  compact 
plates,  an  inner  and  an  outer,  fitting  close  to  the  roots  of  the 
teeth,  between  which  is  the  looser  cancellated  portion  sur- 
rounding the  roots  of  the  teeth,  and  within  which  the  more 
compact,  shell-like  cases  surrounding  the  roots  are  contained. 
The  whole  arrangement  of  the  jaws,  both  with  reference  to 
each  other  and  to  the  remaining  portions  of  the  face  and 
skull,  is  such  as  to  withstand  the  strain  of  muscular  con- 
tractions in  chewing,  and  at  the  same  time  protect  against 
forces  from  without,  such  as  blows,  by  diffusing  them  in 
a  way  to  prevent  their  being  transmitted  to  the  brain  case 

(27). 

As  already  intimated  in  a  previous  paragraph,  the  develop- 
ment of  the  jaws  begins  very  early  in  the  embryo.  Accord- 
ing to  Quain's  Anatomy  (71),  the  order  for  the  begin- 
ning of  calcification  of  the  bones  is  :  first,  the  clavicle ;  second, 
the  inferior  maxillary  (mandible)  ;  and  third,  the  superior 
maxillary  (maxillae).  The  Text-Book  of  Cunningham  places 
the  beginning  at  about  sixth  or  seventh  week  of  foetal  life 
(28,  pp.  144-5).  Witzel  would  seem  to  agree  as  to  time, 
since  he  published  a  plate  (98,  plate  3),  showing  calcification 
of  the  mandible  in  a  foetus  of  six  weeks. 

In  case  of  either  jaw,  calcification  begins  in  a  number  of 
centers  which  later  unite.  The  final  completion  of  this 
process  does  not  occur  in  the  mandible  until  some  time  after 
birth  (usually  during  the  course  of  the  first  year),  when  the 
two  halves  unite. 

Extended  and  accurate  investigations  of  the  growth  of  the 
jaws  from  this  time  until  the  beginning  of  second  dentition 
are  very  few.  On  a  few  points,  however,  authorities  seem 
to  be  in  agreement,  so  that  we  may  characterize  in  a  general 
way  the  principal  developmental  features  of  this  period. 
Naturally  we  turn  first  to  longitudinal  growth.  After  the 
completion  of  the  first  year,  or  at  least  after  the  completion 
of  first  dentition,  there  is  little  or  no  growth  in  those 
portions  of  the  arches  containing  the  temporary  teeth.  If 
any  occurs  at  all  it  is  very  small  in  amount.  With  the 
appearance  of  the  teeth  there  is  a  lengthening  of  the  ascend- 
ing portions  of  the  lower  jaw,  thus  making  room  for  the 
teeth  and  their  alveolar  borders.  The  relationship  of  this 
development  to  the  order  of  the  appearance  of  the  teeth  con- 
stitutes one  of  the  nice  adjustments  of  nature,  as  Pedley  and 


PHYSIOLOGICAL    AGE   AND   SCHOOL    ENTRANCE  297 

Harrison  (63,  p.  42)  have  pointed  out.  In  general,  the  order 
of  tooth  appearance  is  from  front  to  back.  By  this  means 
time  is  gained  for  the  growth  in  the  length  of  these  branches, 
while  at  the  same  time  there  is  not  left  an  "  open  bite  "  in 
the  middle  of  the  arch. 

As  regards  internal  structure,  arrangement  of  the  fine  bony 
particles  or  trabeculae  remains  for  the  most  part  regular, 
though  there  are  some  changes  having  to  do  with  strengthen- 
ing the  jaws  and  adjustment  to  the  developing  crowns  of 
the  permanent  teeth  (98). 

The  rapid  growth  of  the  jaws  at  the  time  of  second  den- 
tition is  a  well  known  fact.  It  is  evident  in  the  changed  pro- 
portions of  both  jaws  and  face,  with  the  resulting  change  in 
facial  expression,  and  is  also  inferred  from  the  fact  that  the 
second  set  contains  a  greater  number  and,  to  all  appearances, 
larger  teeth. 

Growth  is  largely  dependent  upon  the  development  of  the 
teeth,  and  is  therefore  not  uniform  in  all  parts  of  the  jaws. 
A  number  of  investigators  have  attempted  to  answer  the 
question  as  to  whether  there  is  any  longitudinal  growth  in 
those  portions  of  the  arches  bearing  the  temporary  or  decidu- 
ous teeth  at  the  time  of  second  dentition.  Zsigmondi  (106) 
reports  the  results  from  a  long  series  of  these  investigations, 
and  in  addition  describes  an  investigation  of  his  own,  in 
which,  by  the  use  of  plaster  casts,  he  employed  a  new  method, 
obtaining  records  of  the  same  jaws  at  different  stages  of  their 
development. 

Difficulties  of  method  are  everywhere  apparent,  not  the 
least  of  which  is  that  the  measurements  give  a  record,  not  of 
the  differences  in  the  basic  part  of  the  jaw,  but  rather  of  those 
in  the  dental  arch  or  the  alveolar  border  only.  Re- 
ferring in  part  to  the  results  reported  by  Zsigmondi,  in  part 
to  the  original  articles  themselves,  and  comparing  carefully, 
it  seems  only  safe  to  say  that  there  is  not  conclusive  evidence 
that  any  longitudinal  growth  occurs  in  that  portion  of  the 
alveolar  arch  lying  between  the  first  permanent  molars  during 
the  period  of  second  dentition.  Since  this  is  true,  there  is 
likewise  no  evidence  to  show  that  longitudinal  growth  occurs 
in  the  basic  portions. 

That  the  dental  arch  in  the  upper  jaw  becomes  larger  is 
not  disputed,  but  attention  is  called  to  the  fact  that  here  the 
teeth  with  their  alveolar  border  slant  outward,  while  in  the 
lower  jaw  they  slant  rather  inward,  so  that  the  question  of 
longitudinal  growth  of  the  basic  part  of  the  jaw  is  still  left 
unanswered.  Besides,  the  question  as  to  the  presence  or 
absence  of  growth  is  most  often  raised  with  reference  to  the 


2Q8  PHYSIOLOGICAL   AGE   AND   SCHOOL   ENTRANCE 

lower  jaw,  the  result  being  that  most  investigations  have  had 
to  do  with  it,  and  have  secured  data  pointing  more  or  less  to 
conflicting  conclusions.  However,  while  conclusive  proof  is 
lacking,  there  is  not  general  agreement  that  growth  does  not 
occur.  More  recently  Cryer  (27,  p.  14),  who  bases  his  con- 
clusion upon  the  study  of  the  anatomical  arrangement  of  the 
inner  structure  of  the  mandible,  has  declared  in  favor  of 
growth.  Angle  also  seems  to  hold  this  view  (i,  p.  91). 

While  growth  in  the  "  deciduous  arch  "  is  still  questioned, 
on  one  other  point  authorities  are  agreed.  While  the  perma- 
nent incisors  and  canines  require  a  greater  amount  of  space 
than  their  predecessors,  the  greater  requirement  is  partially 
compensated  for  by  a  lesser  space  requirement  on  the  part  of 
the  permanent  bicuspids,  which  are  smaller.  The  actual  need 
for  growth  in  these  portions  of  the  jaws  is  therefore  much 
less  than  it  would  be  were  the  permanent  teeth  uniformly 
larger  than  their  predecessors.  The  compensation  is  much 
less  nearly  complete  in  the  upper  than  in  the  lower  jaw,  thus 
giving  a  second  partial  explanation  of  the  fact  that  the  upper 
permanent  dental  arch  is  apparently  larger,  while  the  increase 
in  the  size  of  the  lower  is  questioned. 

Let  us  turn  attention  next  to  the  posterior  portions  of  the 
jaws.  It  should  be  noted  first  that  authorities  generally  agree 
that  growth  of  these  portions  is  dependent  upon  the  develop- 
ment and  eruption  of  the  molar  crowns.  In  either  jaw  the 
growth  must  be  sufficient  to'  make  room  for  the  three  molar 
teeth  on  each  side.  The  development  of  these  crowns  seems 
to  be  the  signal  for  growth  of  this  portion  of  the  jaws.  This 
is  especially  noticeable  in  the  lower  jaw.  "  The  cutting  of  the 
first  molar  tooth  and  the  formation  of  the  crown  of  the  second 
cause  in  the  following  years  of  life  a  strong  longitudinal  growth 
of  the  maxillary  body,  .  .  ."  writes  Witzel  (98,  p.  59). 

As  in  case  of  the  anterior  portions  of  the  arches,  there  is 
much  disagreement  as  to  the  exact  process  by  which  the 
increase  is  brought  about.  Some  authorities,  such  as  Cryer, 
hold  that  growth  is  general  along  the  jaw  and  that  each  erupt- 
ing crown  pushes  the  ones  anterior  to  it  forward  (27,  p.  14). 
Others  take  the  position  that  the  growth  is  only  at  the  ex- 
treme posterior  portion,  and  that  much  of  it  is  due  to  absorp- 
tion and  deposition  of  the  bone  substance.  Humphry  quotes 
Tomes  (48,  p.  3,  footnote)  to  the  effect  that  these  processes 
are  shown  by  the  examination  of  the  histological  structures 
at  time  of  growth.  Humphry  also  tested  the  growth  in  the 
lower  jaws  of  young  pigs  by  piercing  the  ascending  portions 
and  tying  wires  about  the  anterior  and  posterior  borders. 
Later,  when  the  pigs  were  killed,  the  wires  at  the  anterior 


PHYSIOLOGICAL    AGE   AND   SCHOOL    ENTRANCE  299 

border  were  found  to  have  either  become  loosened  or  dropped 
out,  showing  that  resorption  of  bone  had  taken  place,  while 
the  wires  at  the  posterior  borders  were  found  in  deeply  in- 
dented notches  formed  from  the  progressive  deposition  of 
bone  above  and  below  them  (48,  p.  3  if.). 

Besides  the  horizontal  growth  in  the  arches  of  the  jaws, 
adjustment  to  the  greater  space  required  between  them  to 
accommodate  the  larger  permanent  set  is  accomplished  by 
means  of  a  growth  in  the  length  of  the  ascending  portions, 
or  rami,  of  the  mandible.  With  the  longitudinal  growth  down- 
ward and  backward  the  angle  of  the  jaw  becomes  more  acute, 
approaching  a  right  angle,  though  this  is  apparently  due  in 
part  also  to  the  development  of  the  teeth  and  alveolar  border. 

Finally  there  may  be  mentioned  a  group  of  changes  of  inner 
structure.  Rearrangement  of  the  teeth  brings  about  a  neces- 
sary redistribution  of  their  neural  and  vascular  supply.  In- 
crease of  masticatory  surface,  accompanied  by  a  growth  in 
strength  of  the  muscles  used  in  mastication,  causes  a  strength- 
ening of  the  basic  portions  of  the  jaws ;  lastly,  as  a  result  of 
rearrangement  of  the  lines  along  which  the  forces  are  exerted 
in  mastication,  as  well  as  of  growth,  there  occurs  a  new 
arrangement  of  the  bony  trabeculae  within  the  jaws  to  adapt 
to  the  new  conditions. 

In  addition  to  that  of  the  jaws,  some  other  developmental 
factors  appear  to  be  very  closely  related  to  dentition.  Pos- 
sibly most  prominent  among  these  is  the  growth  of  the  face, 
due  in  part,  of  course,  to  the  increasing  size  of  the  jaws. 
West  found  in  his  Worcester  investigation  (97)  that  there 
are  pretty  distinct  periods  in  the  development  of  the  female 
face,  the  first  division  point  being  at  about  the  seventh  year. 
Transitions  from  one  type  to  the  one  next  following  seemed 
to  be  rather  abrupt.  Rose  found  from  head  and  face  meas- 
urements of  more  than  45,000  children  of  different  nation- 
alities that  the  face  lengthens  much  more  rapidly  during  the 
time  of  change  of  teeth  than  it  does  in  later  years  (75,  p. 
711).  Facial  index  increased  in  length  some  three  and  one- 
half  degrees  between  ages  seven  and  thirteen  (75,  Table  5, 
p.  706). 

Greater  masticatory  ability  seems  to  be  accompanied  by 
an  inner  psychic  change.  Bell  (7)  found  in  his  study  of  the 
psychology  of  foods  that  taste  becomes  "  mentalized "  at 
about  the  age  of  seven  as  it  has  never  been  before.  He  speaks 
of  this  as  a  stage  of  "  teasing  to  taste."  He  found  also  a 
tendency  to  make  every  possible  mixture  at  this  period,  and 
an  increased  interest  in  medicine,  with  a  tendency  to  taste  it. 

Dr.  Wright  (100)  finds  that  periods  of  enlargement  of  the 


3OO  PHYSIOLOGICAL   AGE    AND    SCHOOL    ENTRANCE 

tonsils  without  inflammation  coincide  with  the  times  when  the 
groups  of  molars  are  erupting.  He  finds  that  after  giving 
the  tonsil  prophylactic  treatment,  when  necessary,  and  wait- 
ing for  the  tooth  to  erupt,  the  return  of  the  enlarged  tonsil 
to  the  normal  will  follow  in  a  high  percentage  of  cases.  Dis- 
appearance of  abnormal  tonsilar  conditions  also  follows  the 
treatment  of  carious  teeth  in  many  cases. 

He  contends  that  tonsilar  enlargement  without  infection  is 
but  an  expression  of  the  normal  functioning  of  lymphoid 
tissues  in  that  region,  especially  active  at  times  of  tooth  erup- 
tion because  of  additional  requirements  in  the  way  of  caring 
for  waste  material  which  results  from  rapid  bone  resorption, 
etc.  The  second  period  when  this  condition  is  liable  to  be 
present  coincides  with  that  for  the  eruption  of  tr\e  first  per- 
manent molars,  and  therefore  in  a  general  way  also  with 
the  period  of  life  in  which  we  are  here  especially  interested. 

One  hesitates  to  leave  this  topic  without  dwelling  for  em- 
phasis upon  the  importance  of  dentition  for  development  at 
the  beginning  school  age.  Referring  to  the  relationship  of 
the  teeth  to  nutrition,  Crampton  (26,  p.  354)  has  spoken  of 
tooth  appearance  as  "  the  indication  of  successful  growth  and 
the  earnest  of  further  preparation  for  growth." 

Again,  importance  of  dentition  stands  out  clearly  when  one 
takes  into  account  the  number  of  conditions  by  which  its 
progress  is  affected.  The  great  variation  in  time  of  appear- 
ance has  been  noted.  There  are  many  explanations  for  this. 
Early  or  late  dentition  have  often  been  charged  up  to  here- 
dity, and  facts  regarding  the  first  set,  such  as  those  presented 
by  Holt  (45,  p.  28)  and  Rosenhaupt  (79)  would  seem  to 
indicate  that  there  is  reason  for  doing  so.  Rose  has  found 
that  permanent  teeth  appear  earlier  among  Swedish  than 
among  German  children,  thus  showing  the  influence  of  race 
(77).  He  would  also  credit  the  chewing  of  coarser  foods 
with  some  influence  in  this  case.  Again,  in  the  same  investi- 
gation, Rose  found  dentition  earlier  in  children  of  the  higher 
schools  than  in  those  of  the  Volkschule,  and  earlier  in  chil- 
dren of  city  than  those  of  rural  communities.  This  is  ex- 
plained as  due  to  differences  of  nourishment,  and  to  some 
extent  to  better  racial  selection  also.  The  importance  ot 
nourishment  while  the  crowns  are  developing,  therefore  dur- 
ing the  first  five  or  six  years  of  life,  is  emphasized  by  many 
authorities.  Bell  (7),  without  giving  his  authority,  states 
that  it  is  reported  southern  children  erupt  their  teeth  earlier 
than  northern.  Finally,  it  is  recognized  that  diseases  influ- 
ence dentition.  Holt  (45,  p.  28)  says  syphilitic  children  are 
prone  to  early  dentition,  in  which  case  rapid  decay  is  likely 


PHYSIOLOGICAL   AGE  AND   SCHOOL    ENTRANCE  301 

to  follow.  Rickets  is  usually  credited  with  having  a  retarding 
influence.  Rose  tested  this  (77,  p.  569)  by  comparison 
of  children  with  normal  teeth  and  those  with  hypoplasia,  or 
deficiency  of  enamel.  Among  10,020  children,  he  found  a 
slightly  later  eruption  time  in  the  latter  group.  Latest  denti- 
tion is  seen  in  cretinism  (45,  p.  29). 

The  complexity  of  the  problem  is  evident.  Berten  says 
(8,  p.  267)  that  whoever  has  given  only  slight  attention  to  the 
eruption  of  the  teeth  will  have  found  that  the  time  varies 
with  race,  climate,  sex,  constitution  and  disease,  and  in  part 
to  sports  of  nature. 

Composition  of  the  tooth  crowns  is  apparently  affected  by 
many  of  the  same  influences,  especially  conditions  of  nourish- 
ment and  disease.  Lack  of  lime  in  food  and  water  may  cause 
poor  dental  structures,  with  deficient  enamel,  and  therefore 
poor  protection.  Dr.  Burnham  (18,  pp.  296-7)  reports  a 
number  of  investigations  indicating  that  regions  poor  in  lime 
show  a  high  percentage  of  carious  teeth.  Pedley  and  Harri- 
son (63,  p.  47)  emphasize  the  use  of  the  teeth  as  beneficial, 
in  that  it  increases  blood  supply  and  thus  brings  more  nour- 
ishment. The  disease  of  rickets  apparently  deprives  the  teeth 
of  sufficient  lime  salts,  being  accompanied  usually  by  hypo- 
plasia, a  condition  in  which  the  enamel  is  deficient. 

Finally,  we  may  cite  the  response  of  the  organism  to  dental 
conditions,  as  evidence  of  the  importance  of  the  latter  at 
the  school  age.  Among  others,  Jessen  (50,  p.  i)  quotes  these 
conclusions  from  Rose's  "  Zahnverderbmss  und  Zensur " 
(Deuts.  Monats.  /.  Zahnheilk.,  1904)  : 

"  J.  The  physical  development  of  school  children  is  greatly 
influenced  by  defective  teeth.  2.  The  poorer  the  physical 
development,  the  poorer  also  is  the  mental  power  ("  Spann- 
kraft")  of  the  children,  j.  The  poorer  the  teeth,  the  worse 
are,  on  the  average,  the  grades  of  the  children."  In  his  arti- 
cle on  the  "  Hygiene  of  the  Teeth "  Dr.  Burnham  writes 
(18,  p,  298)  :  "  Of  the  various  disorders  frequently  caused  or 
aggravated  by  decaying  teeth  are  not  only  enlarged  glands 
of  the  neck,  headache,  neuralgia,  earache,  but  indigestion, 
heart  trouble,  irritation  of  the  nervous  system,  epilepsy,  and 
perhaps  chorea  and  other  neuroses." 

Preservation  of  a  full  set  of  sound  temporary  teeth  and 
regulation  of  their  positions  when  necessary  are  requisites  for 
proper  development  of  both  teeth  and  jaws  at  time  of  second 
dentition.  Premature  extraction,  too  long  retention,  caries  or 
malocclusion  in  case  of  the  temporary  set  may  be  the  cause 
of  improper  development  of  the  jaws  with  impaction  or  with 
abnormalities  in  position  of  the  permanent  crowns. 


3<32  PHYSIOLOGICAL   AGE   AND    SCHOOL    ENTRANCE 

Some  experiments  upon  animals  would  seem  to  indicate 
the  dependence  of  proper  development  in  jaws  and  face  upon 
a  full  set  of  functioning  teeth.  Walkhoff  (92)  cut  one  tem- 
poral muscle  of  a  dog  four  weeks  old,  compelling  him  to 
chew  only  on  the  other  side.  Within  three  months  a  differ- 
ence between  the  development  of  the  two  sides  of  the  jaws 
could  be  detected,  and  at  the  end  of  a  year  the  functioning 
side  was  much  larger  and  stronger  than  the  other.  Dr.  Baker 
(5)  performed  a  similar  experiment  by  grinding  the  teeth  of 
young  rabbits,  preventing  occlusion  in  one-half  of  the  jaw. 
Not  only  the  jaws,  but  the  parts  of  the  skull  to  which  the 
muscles  of  mastication  were  attached  showed  the  effects  by 
their  greater  size  and  strength  on  the  functioning  side.  The 
unused  sides  remained  undeveloped.  The  prepared  skulls 
showed  a  distinct  asymmetry. 

While  emphasizing  the  point  that  the  presence  of  all  the 
teeth  is  essential,  Dr.  Angle  has  stated  (i,  p.  17)  that,  "  in 
function  and  influence  some  are  of  greater  importance  than 
others,  the  most  important  of  all  being  the  first  permanent 
molars."  He  explains  further  that  this  is  true  because,  i. 
they  are  largest  and  firmest  in  their  attachment,  2.  they  have 
the  most  important  location  in  the  arches,  5.  their  length  de- 
termines the  separation  of  jaws  and  length  of  bite,  thus 
contributing  to  facial  proportions,  4.  they  are  first  in  position 
and  influence  other  tooth  positions,  and  5.  they  are  most 
constant  in  time  of  eruption  and  in  the  assumption  of  normal 
positions. 

From  all  these  facts,  and  especially  in  view  of  the  close 
relationship  of  tooth  development  and  nutrition,  it  must  fol- 
low that  dentition  is  a  matter  of  prime  importance  in  the 
early  years.  It  would  perhaps  not  be  too  much  to  say  that, 
from  among  all  the  factors  which  may  and  should  be  con- 
sidered for  such  a  purpose,  dentition  is  the  best  single  indi- 
cator of  the  stage  of  physical  development  which  a  child 
has  reached  at  any  time  during  these  early  years,  or,  as  some 
woujji  state  it,  of  physiological  age. 

Having  dwelt  somewhat  at  length  upon  this  very  import- 
ant phase  of  development,  we  may  bring  together  the  prin- 
cipal points  in  this  brief  summary: 

i.  The  development  of  the  teeth  and  the  parts  closely  re- 
lated to  them,  particularly  the  jaws,  give  evidences  of  a 
transitional  stage  at  about  the  time  of  the  beginning  school 
years.  The  loss  of  the  temporary  and  the  eruption  of  the 
second,  permanent,  more  numerous,  adult-sized  set  of  teeth 
is  begun  at  this  time,  producing  a  new,  different  method  of 


PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE  303 

articulation.  This  is  accompanied  by  rapid  growth  in  certain 
portions  of  the  jaws,  with  considerable  rearrangement  of  the 
inner  structures,  resorption  and  deposition  of  bone  sub- 
stance, etc. 

2.  Normally,  the  transition  is  begun  by  the  eruption  of 
the  first  permanent  molars,  at  about  the  seventh  year,  after 
which  temporary  tooth  groups  are  replaced  by  the  perma- 
ment  in  the  order ;  inner  incisors,  outer  incisors,  first  bicus- 
pids, with  canines  and  second  bicuspids  following  in  variable 
order,  and  followed  in  turn  by  second  molars.  Wisdom  teeth 
come  much  later. 

j.  The  time  of  tooth  appearance  in  different  children 
shows  considerable  variability,  beginning  with  the  early  years, 
clearly  evident  at  the  time  the  first  molars  erupt,  and  increas- 
ing rapidly  with  the  progress  of  dentition  thereafter. 

4.  Sex  differences  are  apparent  in  the  eruption  time  of  the 
permanent  teeth,  those  of  the  girls  appearing  earlier,  on  the 
average,  than  those  of  boys.     Here  also,  the  difference  in- 
creases with  the  progress  of  dentition. 

5.  The  vital  significance  of  dentition  as  a  factor  in  develop- 
ment is  shown  by  its  close  relationship  to  nutrition,  by   its 
close  relationship  to  the  growth  of  other  parts,  such  as  jaws, 
face  and  skull ;  by  the  many  influences,   such  as  nutrition, 
race,  sex,  etc.,  by  which  it  is  influenced ;  and  by  the  reaction 
of  the  organism  to  dental  conditions   as  shown  in  physical 
development,  mental  power,  and  the  like. 

6.  These  things   being  true,   it   follows   that  the   state  of 
advancement  reached  in  dentition  is  a  good  indication  of  the 
stage  of  progress  which  a  child  has  reached  in  his  total  physi- 
cal development.     The  transitional  features  described  there- 
fore take  on  an  additional  significance. 

Growth  of  the  Skull. — The  period  of  life  under  considera- 
tion is  apparently  transitional  as  regards  the  growth  of  the 
skull.  In  Quain's  Anatomy  (70,  p.  82)  we  read: 

"  The  skull  grows  rapidly  during  the  first  seven  years  of  life.  By 
that  time,  certain  parts,  including  the  circumference  of  the  occipital 
foramen,  the  body  of  the  sphenoid,  the  cribriform  plate,  and  the  petrous 
division  of  the  temporal  have  attained  their  definitive  size.  The 
other  regions  also  increase  but  little  until  the  approach  of  puberty, 
when  a  second  period  of  active  growth  begins,  affecting  especially 
the  face  and  frontal  portion  of  the  cranium,  with  which  is  associated 
the  expansion  of  the  frontal  and  other  air  sinuses." 

These  facts  become  the  more  interesting  when  we  recall 
that  cessation  of  growth  in  these  portions  occurs  at  just 
about  the  same  time  as  the  beginning  of  more  rapid  growth 


304  PHYSIOLOGICAL   AGE   AND   SCHOOL   ENTRANCE 

in  parts  of  the  face,  as  previously  described,  and  as  demon- 
strated by  West  (97)  and  by  Rose  (75). 

Groivth  of  the  Brain. — Data  with  regard  to  the  size  of 
the  normal  brain  at  different  stages  of  development  are 
meagre.  Aside  from  this,  there  are  many  difficulties  which 
arise  from  unavoidable  inaccuracies  in  methods  of  sectioning 
and  preparing  specimens,  and  also  from  the  fact  that  indi- 
vidual variations  are  great.  Averages  of  brain  weights  are 
therefore  of  doubtful  value. 

It  is  generally  agreed  that  the  early  years  are  years  of  very 
rapid  gain  in  brain  weight.  There  are  no  data,  however,  to 
show  beyond  question  that  a  distinct  nodality  occurs  at  the 
beginning  of  the  later  childhood  period.  Curves  for  brain 
weights  at  different  ages  can  only  be  said  to  suggest  that 
this  is  true.  Pfister  is  reported  to  have  found  that  the  brain 
weight  at  the  end  of  the  sixth  year  is  not  infrequently  equal 
to  that  ot  the  adult  (71,  p.  342).  This  is  also  observable  in 
the  tabulation  of  brain  weights  collected  by  Vierordt  (90, 
pp.  36-37).  Donaldson,  in  his  study  of  the  brain  was  led  to 
conclude,  largely  on  the  basis  of  the  curve  for  brain  weights 
collected  by  Vierordt,  that,  ".  .  .  .By  the  seventh  year  the 
encephalon  has  reached  approximately  its  full  weight,  the  sub- 
sequent increase  being  comparatively  small  .  .  ."  (30,  p.  104). 
We  may  say,  therefore,  not  that  brain  weights  show,  but 
rather  that  they  suggest  a  transition  from  rapid  gain  in  gross 
weight  to  a  different  mode  of  development  from  the  'school 
age  onward.  This  suggestion  is  strengthened  by  the  fact  that 
the  rapid  growth  of  the  skull  ceases  at  about  the  same  time. 
Again,  psychological  investigations  seem  to  show  for  this 
period  a  rapid  development  of  muscular  control,  and  the  like, 
suggesting  development  along  the  line  of  better  inner  organi- 
zation rather  than  by  means  of  mere  addition  of  material. 

Development  of  the  Eye. — Embryonically,  the  eye  develops 
as  a  specialized  portion  of  the  brain.  It  is  therefore  interest- 
ing to  note  that  there  is  some  indication  of  its  having  attained 
approximately  adult  size  at  the  same  time  with  the  brain. 
Stratz  (86,  a)  has  noted  the  relatively  large  size  of  the  eye 
as  compared  to  the  small  face  of  the  child  in  the  early  years, 
due  in  part,  of  course,  to  the  rather  late  development  of  the 
facial  portions.  The  statement  of  Merkel  would  indicate  that 
there  is  a  further  possible  explanation.  Without  giving  data, 
he  says  (55,  Vol.  I,  p.  256)  :  "  In  connection  with  the  de- 
velopment of  the  whole  eye-ball,  it  occurs  that  the  horizontal 
breadth  of  the  iris  is  already  reached  in  the  sixth  year  of 


PHYSIOLOGICAL    AGE   AND    SCHOOL    ENTRANCE  305 

life."  Parallel  to  this  fact  —  provided  data  may  be  found  to 
support  it  as  fact,  —  there  occurs  at  about  the  school  en- 
trance age  a  transition  in  power  to  use  the  eye  and  also  to 
control  its  movements. 

An  important  factor  is  the  power  to  employ  binocular 
vision.  In  this  is  involved  the  ability  to  "  fuse  "  the  slightly 
different  images  from  the  two  eyes  and  interpret  them  as  one 
object.  This  begins  in  the  first  few  weeks  of  life,  and  accord- 
ing to  Miss  Sayer  (82),  is  usually  complete  about  the  sixth 
to  ninth  year  of  life.  In  learning  to  overcome  the  difficulty, 
the  child  has  a  tendency  to  "  squint,"  but  overcomes  it  after 
learning  to  use  the  eyes  properly.  From  defects  of  vision, 
however,  he  may  develop  a  permanent  "  squint."  This  is 
easily  cured  by  means  of  the  amblioscope  if  taken  before  the 
age  of  six,  but  otherwise  it  develops,  as  does  stammering, 
into  a  pathological  condition  that  is  very  difficult  to  cure.  The 
statement  of  Dr.  Cornell  (23,  p.  243)  with  regard  to  this  con- 
dition is  in  agreement  with  that  of  Miss  Sayer.  Again,  while 
largely  dependent  upon  central  brain  structure,  there  should 
be  mentioned  in  this  connection  the  lack  of  power  to  retain 
visual  imagery  in  case  of  those  persons  who  become  blinded 
earlier  than  the  fifth  to  seventh  year  (49). 

Here,  again,  phenomena  which  apparently  involve  both 
visual  organs  and  visual  brain  centers  would  seem  to  suggest 
strongly  that  the  closing  years  of  earlier  childhood  constitute 
a  time  of  change,  both  with  respect  to  structural  development 
and  functioning. 

Larynx  and  Voice.  —  Vocal  organs  and  vocal  powers  give 
evidence  of  a  nodality  of  development  at  beginning  of  the 
later  childhood  period.  Of  the  larynx  Earth  (6,  p.  86) 
writes  : 

"  In  the  first  two  years  of  life  the  growth  of  the  larynx  is  very 
slight.  With  the  active  use  of  speech  in  the  following  years  the 
growth  progresses  more  rapidly.  It  appears,  however,  to  be  limited 
more  to  the  muscles  that  move  the  vocal  cords.  From  the  sixth  to 
the  fourteenth  year  of  life  the  growth  of  the  larynx  is  almost  sta- 
tionary again,  or,  if  it  is  present,  is  very  slightly  noticeable,  strikingly 
and  disproportionately  less  noticeable  than  the  growth  of  the  remain- 
ing organs  of  the  body." 

Cunningham's  Anatomy  makes  a  similar  statement  (28,  p. 


"  In  the  newly  born  child,  the  larynx,  in  comparison  with  the  rest 
of  the  body,  is  somewhat  large  (  -  )  and  it  continues  to  grow 
slowly  and  uniformly  up  to  the  sixth  year  of  childhood.  At  this 
period  there  is  a  cessation  of  growth,  which  persists  until  puberty 
is  reached,  and  then  a  stage  of  active  growth  supervenes." 


3o6 


PHYSIOLOGICAL   AGE   AND   SCHOOL   ENTRANCE 


Gutzmann's  diagram  of  the  averages  for  normal  children 
of  both  sexes  up  to  the  age  of  fifteen  (37,  p.  51)  indicates 
a  rapid  widening  of  the  range  of  voice,  beginning  at  the  age 
of  seven.  Differentiation  of  the  sexes  is  also  shown  at  this 
time,  the  range  for  girls  being  wider  than  that  for  boys  from 
this  age  onward.  The  diagram  is  as  follows. 


i 


1-2 


t?+ 


3-5 


i 


10 


fr 

11 


13 


14- 


15 


N euro-muscular  Control. — Differences  in  the  power  to  con- 
trol bodily  organs  indicate  a  transitional  period  at  six  or  seven 
years.  Speech  development  also  gives  such  an  indication. 
Apparently  this  period  marks  a  stage  of  completion  in  speech 
coordinations,  since  infantile  babble,  if  continued  after  this 
time,  is  usually  considered  pathological  (22).  Control  of 
visual  organs,  as  previously  described,  gives  a  similar  indica- 
tion. Unless  corrected  before  this  period,  "  squint "  becomes 
permanent.  Vocal  power,  on  the  other  hand,  as  indicated  by 
the  range  within  which  pure  tones  can  be  sung,  shows  a  rapid 
increase  from  this  time  on  (37).  The  two  sexes  also  show  a 
difference  in  breadth  of  range  from  this  period  onward,  at 
least  up  to  the  pubescent  years.  Bryan's  tests  of  precision  in 
finger  movements  (14)  snowed  that  in  both  the  "  up  "  and 
"  down  "  writing  movements  almost  half  the  gain  between  the 
ages  of  six  and  sixteen  was  made  between  the  ages  of  six 
and  eight  years.  Halleck  has  stated,  "  The  vital  time  for 
motor  training  is  before  the  age  of  eight "  (40,  p.  835). 

Pathological  Conditions. — Some  pathological  conditions 
may  be  grouped  together  to  show  a  relationship  to  this  period 
of  life.  Stuttering,  which  differs  somewhat  from  the  infantile 
babble  previously  referred  to,  has  been  shown  to  be  more 
prevalent  at  seven  to  eight  years  of  age.  Conradi  (22)  be- 
lieves there  is  a  causal  connection  between  this  and  dentition. 
Jastrow  (49)  found  among  some  200  persons  in  institutions 
for  the  blind  that  those  who  had  lost  the  power  of  sight 
previous  to  the  age  five  to  seven  years  did  not  retain 
visual  imagery  in  their  dreams  in  after  years.  Those 
blinded  later  than  the  age  of  seven,  on  the  other  hand,  did 
retain  visual  imagery.  Clouston,  in  his  "  Neuroses  of  Devel- 
opment "  (2iy2),  long  ago  observed  that  the  age  of  seven  or 
eight  is  a  time  when  many  neuropathic  conditions  are  liable  to 


PHYSIOLOGICAL    AGE   AND    SCHOOL    ENTRANCE  307 

break  out.  In  this  connection  again  should  be  mentioned  that 
"  squint,"  also  infantile  babble  are  but  natural  when  occur- 
ring previous  to  this  age,  while  if  lasting  longer  they  seem 
to  be  so  deeply  grounded  as  to  constitute  pathological  condi- 
tions. 

These  are  by  no  means  proofs,  nor  is  the  list  complete,  yet 
the  suggestion  is  strong  that  after  this  period  of  life  the 
physical  organization  is  somewhat  different  from  that  which 
precedes. 

Mental  Development. — Adequate  treatment  of  this  topic 
would  make  this  paper  far  too  voluminous.  We  can  touch 
it  but  briefly,  stopping  only  for  some  general  statements, 
chiefly  concerning  its  relationship  to  our  problem. 

Early  years  have  long  been  recognized  as  a  time  of  sensory 
training,  shorter  attention  span,  shorter  memory  span,  etc., 
but  no  sharp  transition  has  been  clearly  shown.  Mental  tests 
are  not  yet  sufficiently  refined  to  grade  accurately  small  steps 
of  advancement.  Individual  variations  are  too  great. 

Though  evidence  to  the  contrary  may  be  found,  that  there  is 
a  correlation  of  mental  and  physical  development  during 
school  life  has  been  indicated  in  a  general  way  by  such  in- 
vestigations as  those  of  Porter  (67),  Smedley  (84),  Quirsfeld 
(72)  and  Crampton  (26).  Methods  of  grading  mental  ad- 
vancement with  reference  to  stage  of  physical  development 
rather  than  chronological  age  at  this  period,  however,  have 
yet  to  be  worked  out.  There  is  needed  here  much  further 
investigation,  on  the  individual  plan,  for  the  purpose  of  find- 
ing the  degree  of  mental  advancement  that  may  be  expected 
in  a  pupil  of  either  sex  who  has  reached  a  given  stage  in  his 
or  her  physical  development.  The  question  arises  as  to 
whether  such  investigation  might  not  show  a  characteristic 
of  mental  development  corresponding  to  the  transitions  in  the 
physical.  Facts  of  brain  growth,  neuro-muscular  control  and 
the  like  suggest  that  this  might  be  true. 

Summary. — By  way  of  summary  we  may  generalize  with 
regard  to  the  preceding  facts  bearing  on  the  question  of 
nodality  at  the  school  entrance  period  as  follows : 

j.  Disturbances  of  growth  in  height  and  weight  have  been 
noticed  at  this  period  but  their  nature  is  imperfectly  under- 
stood. 

2.  Dentition  shows  distinctly  a  transition  at  this  period,  and 
because  of  close  relationship  to  other  phases  of  development 
suggests  strongly  that  it  is  general  in  its  nature. 

5.  Both  skull  and  brain  show  a  change  in  growth  rate  at 
about  this  time  of  life. 


308  PHYSIOLOGICAL  AGE   AND   SCHOOL   ENTRANCE 

4.  Growth  of  larynx  and  development  of  voice  range  indi- 
cate transition  in  these  years. 

5.  The    statements    of    some    authorities    with    regard    to 
growth  of  the  eye  and  control  of  its  movements  suggest  nodal- 
ity  in  its  development  at  this  age. 

6.  Phenomena   of   muscular   control,   also   facts   regarding 
pathological  conditions,  give  evidence  of  a  change  in  physical 
organization  after  this  period. 

7.  A  clear-cut  mental  transition  has  not  been  shown,  but 
tests  have  not  related  mental  to  physical  stages  of  advance- 
ment.    General  correlations  of  mental  and  physical  powers 
and  facts  regarding  brain  growth  and  muscular  control  sug- 
gest that  tests  relating  these  phases  would  indicate  a  transition 
here  also. 

On  the  basis  of  these  facts  it  appears  that  the  question 
regarding  a  transitional  stage  of  development  at  the  begin- 
ning of  later  childhood  should  be  answered  in  the  affirmative. 
The  time  at  which  these  phenomena  occur  is  of  course  only  ap- 
proximate, being  based  upon  averages  in  most  cases.  The 
degree  to  which  these  changes  are  interdependent  is  also  un- 
known. Whether  they  are  all  secondary  to  one  basal,  radi- 
cal change,  as  for  example  dentition,  or  whether  they  repre- 
sent a  more  general  reorganization  to  which  each  is  related 
cannot  be  stated.  It  seems  probable  that  the  latter  is  the 
case,  although  it  is  a  problem  that  must  be  left  open.  It  is 
certainly  one  that  merits  further  investigation. 


COMPARATIVE  DEVELOPMENT  OF  THE  SEXES. 

If,  now,  we  give  attention  to  the  question  of  the  compara- 
tive development  of  the  two  sexes  at  the  school  age,  we  are 
led  to  the  consideration  of  a  number  of  groups  of  data  simi- 
lar to  those  of  the  preceding  section. 

Occasional  statements  with  regard  to  differences  of  the 
sexes  at  this  early  period  of  life  have  been  made.  Tyler  (88, 
p.  139)  thought  girls  of  six  begin  to  show  signs  of  the  precocity 
which  characterizes  later  development.  Rose  mentioned  dif- 
ferences of  sex  at  time  of  second  dentition  (77,  p.  555). 
Stratz  (86  a)  thought  sex  differences  in  bodily  form  first  be- 
come evident  at  the  age  of  six,  after  which  girls  show  more 
grace  of  curve,  boys  more  of  angularity  and  strength.  For 
the  most  part,  however,  it  has  been  taken  for  granted  that  the 
development  of  the  two  sexes  is  the  same  until  some  time 
after  this  period  of  life  is  passed. 

In  an  article  published  at  a  time  when  this  study  was  near 
completion,  Dr.  Boas  (9)  made  some  comparisons  of  develop- 


PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE  309 

ment,  particularly  in  dentition  and  ossification  of  the  skeleton, 
which  showed  a  greater  advancement  on  the  part  of  girls  at 
this  period.  As  he  has  stated,  however,  the  number  of  data 
was  limited,  and  the  study  rather  of  a  preliminary  nature. 
While  his  conclusions  are  partially  correct,  it  may  still  be 
said  that  no  extended  comparison  of  facts  has  been  made  to 
decide  the  matter  of  comparative  advancement  of  the  physical 
development  in  the  sexes  at  the  beginning  school  period  of 
life.  It  is  our  purpose  here  to  attempt  such  a  comparison. 

Height. — Comparison  of  absolute  height  at  any  given  time 
in  the  early  years  does  not  show  any  cause  for  a  differentia- 
tion of  the  sexes.  The  same  is  true  of  comparisons  where 
added  increments  are  reckoned  as  percentages  of  previously 
attained  height.  A  question  arises,  however,  as  to  whether 
this  is  an  adequate  method  for  getting  at  the  actual  attainment 
for  a  given  age.  At  maturity  the  male  is  considerably  larger 
than  the  female.  Nor  do  they  reach  maturity  at  the  same 
time.  If,  then,  our  final  comparison  is  to  be  one  of  unequals, 
comparisons  previous  to  that  time  should  not  be  on  a  basis 
of  absolute  equality,  else  erroneous  conclusions  will  result. 
What  we  should  ask  is  not,  "  Does  the  height  of  the  boy  equal 
that  of  the  girl  at  a  given  age?"  Rather  should  the  question 
be,  "  What  are  the  percentages  of  final,  adult  height  reached 
in  the  two  cases  at  a  given  age  ?  " 

Comparison  by  such  a  method  has  been  attempted.  In  a 
preliminary  reckoning,  taking  Dr.  Boas'  averages  for  children 
of  larger  American  cities,  as  given  by  Burk  (17,  Table  H.), 
the  average  height  of  boys  at  6.5  years  is  69.88%  of  the  ave- 
rage at  15.5  years,  while  of  girls  it  is  70.35%. 

Results  thus  computated,  on  the  basis  of  data  from  a  num- 
ber of  extended  investigations,  are  given  in  Table  D.  Except 
in  the  last  three  cases,  where  the  references  are  indicated,  these 
are  on  the  basis  of  the  corrected  averages  given  in  Burk's 
"Table  A"  (17).  These  last  three  are  not  the  corrected 
averages.  Since  adult  heights  could  not  be  secured  from  the 
tables,  the  average  at  17.5  years  has  been  chosen  as  repre- 
senting post-pubescent  height. 

Since  girls  'are  nearer  adult  height  at  the  age  of  17.5  years 
than  boys  of  equal  age,  it  is  evident  that  they  are  at  a  dis- 
advantage in  these  comparisons.  Yet  in  every  case  the  indi- 
cation is  that  they  have  attained  a  greater  percentage  of  their 
post-pubescent  height  at  the  age  of  6.5  years  than  boys  of  the 
same  age.  Comparisons  with  averages  of  adult  height  would 
be  more  accurate,  but  it  is  plain  that  they  would  also  show 
greater  differences  of  the  percentages,  thus  making  the  girls 
appear  still  more  advanced,  relatively. 


3io 


PHYSIOLOGICAL   AGE   AND    SCHOOL    ENTRANCE 


TABLE  D. 

PERCENTAGE  OF  POST-PUBESCENT  HEIGHT  ATTAINED  AT 
SCHOOL  ENTRANCE  PERIOD. 


Investigator 

Age 

Com- 
pared 
to 

Percentage  for 

Boys 

Girls 

Bowditch  .    . 

.  (Boston)  

6.5  yrs. 

• 

H 

a 

a 
u 

11 
« 
It 
(I 

8 

ij.Sjrs- 

u 
u 

u 
u 
(( 

u 
u 

16.5  yrs. 
17.5  yrs. 

a 

17 

66.08 
66. 
66  .  10 
58.20 
66  .90 
67  .06 
65.98 
69  .40 
66.46 
65.60 
64  .60 
68.ii 
66  .99 
60.38 
72.89 

70.03 
67  .60 
69  .60 
70.80 
69.70 
70.70 
69.14 
70  .60 
68.60 
66.66 
65.90 
70.40 
70.29 
69.31 
7^-33 

Porter  

.  (St   Louis)  .... 

Peckham  .... 

.  (Milwaukee)  .  . 
.(Oakland).  .  .  . 
.  (Worcester)  .  .  . 

West  

Gilbert 

(New  Haven) 

Gilbert 

(Iowa) 

Key  
Anth.  Com'n. 
Quetelet  

(Sweden)    .... 

.  (England)  .... 
.  (Belgium)  .... 

Pagliani  
Hertel  
1  Smedley  

.  (Turin)  

.  (Denmark)  .  .  . 
.  (Chicago)  

'  Lan^e 

(Germany) 

3Bobbitt  

.(Phil.  Is.)  

See  (84). 


See  (90,  pp.  10-11).         3  See  (12). 


As  a  matter  of  interest,  comparison  of  average  heights  of 
feeble-minded  in  nineteen  institutions,  as  given  by  Goddard 
(35),  was  made,  using  ages  six  and  twenty.  Percentage  of 
twenty-year  height  reached  at  the  earlier  age  was,  for  males, 
66.76,  for  females,  68.82. 

Weight. — As  in  case  of  height,  data  for  the  average  at- 
tainments of  weight  have  not  indicated  any  differences  in  the 
sexes  preceding  the  pubescent  period  of  growth.  Both  Porter 
(66)  and  Burk  (17)  noted  a  slight  superiority  of  boys  during 
the  first  few  school  years.  Applying  the  method  of  compari- 
sons just  used  in  case  of  height,  however,  and  using  again 
the  corrected  averages  from  Burk's  collection  of  data  (17, 
Table  E),  we  obtain  the  results  presented  in  Table  E. 

While  there  is  slight  lack  of  uniformity  in  these  results,  in 
general  it  holds  true  that  there  is  shown  a  superiority  of  girls 
in  the  amount  of  post-pubescent  weight  attained  at  the  ear- 
lier age. 

In  case  of  both  height  and  weight,  therefore,  the  relative 
attainment  of  girls  is  shown  to  be  slightly  superior  to  that  of 
boys  at  about  the  age  of  6.5  years. 

Skeletal  Development. — Radiographic  studies  have  shown 
that  ossification  of  the  skeleton  proceeds  more  rapidly  in  girls 
than  in  boys  during  the  early  years.  This  is  especially  notice- 


PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE  31! 

TABLE  E. 

PERCENTAGE  OF  POST-PUBESCENT  WEIGHT  ATTAINED  AT 
SCHOOL  ENTRANCE  PERIOD. 


Investigator 

Age 

Com- 
pared 
to 

Percentage  for 

Boys 

Girls 

Bowditch 

(Boston) 

6.5  yrs. 

u 

a 
it 

u 

7-5  yrs. 
6.5  yrs. 

u 

17-5/rs. 

u 
If 
(I 
(I 
u 

16.5  yrs. 
i7.5jrs. 

35-45 
35-58 
36.14 
34.35 
34-64 
36.00 
32  .82 
39.60 

39-64 
34.83 
31.66 

33-91 
34.61 

37-48 
35-94 
38.99 
38.04 
38.00 
38.96 
34.38 
39-53 
39-23 
42.37 
34-57 
36.10 

37-J4 

Porter 

(St   Louis)  .  .  . 

.  (Oakland)  .  .  . 
(Milwaukee) 

Peckham 

West  
Gilbert 

.  (Worcester)  .  . 
(New  Haven) 

Gilbert 

(Iowa) 

Kev 

(Sweden)   . 

Hertel 

(Denmark) 

Erismann.  .  .  . 
Pagliani  
Anth.  Com'n  . 
Misawa 

.  (Moskow)  .  .  . 
(Turin) 

.  (England)  
(  TciDciiO 

ft* 

able  in  the  carpal  bones  of  the  wrists  and  the  epiphyses  of  the 
joints.  Dr.  Rotch  makes  this  statement,  but  gives  few  data 
(80,  p.  416).  Pryor's  studies,  however,  give  data  by  which 
this  seems  to  be  clearly  indicated  (69),  though  their  number  is 
limited.  He  quotes  a  conclusion  from  a  previous  paper  by 
himself  as  follows  (69,  p.  3)  :  "  The  bones  of  the  female  os- 
sify in  advance  of  the  male.  This  is  measured  first  by  days, 
then  months,  then  years." 

Choosing  the  trapesoid  bone  of  the  wrist  as  an  example, 
we  may  note  that  he  finds  its  time  for  ossification  to  be  be- 
tween the  fourth  and  fifth  year  in  the  female,  between  the 
fifth  and  sixth  year  in  the  male  (69). 

Dentition. — Differences  in  the  time  of  eruption  of  the 
teeth  should  again  be  emphasized  at  this  point.  Greater  ra- 
pidity in  the  eruption  of  the  teeth  of  girls  was  shown  in  case 
of  each  of  the  investigations  referred  to,  beginning  with  the 
first  molars  and  continuing  up  to  the  time  of  appearance  of 
canines  and  second  molars.  The  difference  is  by  no  means 
as  great,  however,  at  the  first  molar  stage  as  Boas  found 
(9,  p.  815)  from  his  limited  collection  of  data.  Rose's 
averages  show  the  difference  in  time  of  first  molars  to  be  as 
small  as  one  to  two  months.  It  should  be  emphasized  again 
that  the  difference  in  eruption  time  of  the  teeth  grows  pro- 
gressively greater  with  advancement  of  dentition.  By  the  time 
the  second  molars  appear,  the  difference  in  time  between  the 


312  PHYSIOLOGICAL  AGE   AND   SCHOOL   ENTRANCE 

two  sexes  approximates  the  difference  in  time  between  their 
attainment  of  pubescence. 

Growth  of  the  Brain. — The  limited  number  of  data  ren- 
ders comparisons  of  brain  weights  for  the  two  sexes  very 
difficult.  Only  general  indications  may  be  noted.  Curves 
constructed  on  the  basis  of  Vierordt's  data  (30,  p.  105)  seem 
to  indicate  an  earlier  attainment  of  adult  brain  weight  in 
females.  This  can  be  said  to  be  little  more  than  an  indica- 
tion, however,  on  account  of  the  difficulties  of  method  for- 
merly referred  to  and  the  great  variability  in  brain  weights. 

N euro-Muscular  Development. — The  probability  indicated 
by  brain  weights  is  in  correspondence  with  that  indicated  by 
facts  of  muscular  control.  Hancock  found  in  his  swaying 
tests  that  girls  were  more  steady  in  the  early  years  than  boys 
(41).  Automatograph  tests  showed  better  lateral  control  of 
the  arm,  and  tremograph  tests  showed  greater  control  of  fin- 
ger movements  among  girls  also.  Observations  of  less  defi- 
nite tests  again  showed  the  superiority  of  girls  in  control  of 
movements. 

Bryan's  tapping  tests  seem  to  be  alone  in  their  showing 
of  better  control  on  the  part  of  boys.  He  says  (14,  p.  173) 
that  differences  are  slight,  but  that  within  the  narrow  limits 
indicated  there  is  a  slight  superiority  of  boys  over  girls. 

Strength  tests  were  compared  by  Burk  (17)  by  a  method 
similar  to  the  one  we  have  used  for  height  and  weight.  From 
the  data  of  Porter,  Roberts  and  Gilbert  he  found  percentages 
indicating  that  boys  had  attained  1/5  their  sixteen-year 
strength  at  the  age  of  six  years,  1/4  from  six  to  eleven. 
Girls  had  gained  a  greater  percentage  at  six,  and  from  this 
on  their  acquirement  was  more  rapid  than  that  of  boys. 

Gesell  noted  that  boys  as  a  class  show  greater  tendency 
toward  uncoordinated  writing  as  early  as  the  first  grade  and 
up  through  the  high  school  (33). 

In  this  connection  should  be  mentioned  again  that,  begin- 
ning with  the  age  of  seven,  the  range  within  which  pure  tones 
can  be  sung  is  wider  for  girls  than  for  boys. 

Stuttering,  which  begins  most  often  in  the  early  years,  has 
been  found  in  a  number  of  investigations  to  be  more  preva- 
lent among  boys  (22,  p.  361).  Various  ratios  for  the  sexes 
have  been  reported.  Conradi  reports  also  that  girls  learn  to 
talk  earlier  than  boys  (22,  p.  363). 

With  the  exception  of  the  tapping  tests,  all  the  indications 
of  power  of  control  here  enumerated  show  superiority  in  girls. 

Summary. — On  the  basis  of  the  data  here  presented  it 
seems  fair  to  conclude  that  the  physical  development  of  girls 


PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE  313 

is  relatively  more  advanced  than  that  of  boys  at  the  age  of 
five  or  six  or  thereabouts.  On  the  average  they  have  then 
attained  a  greater  percentage  of  their  post-pubescent  height, 
a  greater  percentage  of  their  post-pubescent  weight,  their 
skeletal  development  is  more  advanced,  and  their  dentition 
has  progressed  further.  Aside  from  this  there  is  a  strong 
suggestion  that  a  greater  percentage  of  adult  brain  weight 
has  been  attained  by  them,  and  this  is  supported  by  the  fact 
that  most  data  available  show  a  more  advanced  power  of 
neuromuscular  control.  How  great  the  difference  in  general 
physical  development  is  a  matter  to  be  determined  by  fur- 
ther investigation. 

DISCUSSION,  PEDAGOGICAL  SUGGESTIONS,  AND  SUMMARY 

So  far,  the  aim  has  been  to  find  solutions  for  our  two  main 
problems.  For  the  first  we  may  say  that,  while  not  proved, 
a  great  mass  of  data  indicate  a  transition  in  physical  develop- 
ment at  the  period  of  usual  school  entrance.  Regarding  the 
second  we  may  say  that  greater  advancement  in  the  physical 
development  of  girls  at  this  time  is  pretty  clearly  shown. 

The  solution  or  partial  solution  of  these  two  problems  sug- 
gests a  number  of  others.  If  this  is  a  transitional  period, 
what  is  its  fundamental  nature?  Is  the  transition  general  or 
due  to  a  single  factor,  as  dentition?  That  it  is  the  former 
seems  to  be  the  case,  but  it  is  still  an  open  problem.  In  case 
the  transition  is  not  of  a  general,  fundamental  nature,  then 
a  whole  series  of  problems  regarding  the  relationship  of  these 
several  transitional  phenomena  arise.  For  example,  is  ra- 
pidity of  dentition  to  be  correlated  with  rapidity  of  skeletal 
ossification,  as  Holt  (45)  has  stated  is  the  case  in  infancy? 
Are  disturbances  of  growth  in  height  and  weight  noted  at 
this  period  due  to  conditions  of  dentition  or  do  they  occur 
regardless  of  it? 

The  correlation  of  mental  with  physical  development  at 
this  period  is  a  problem  which  those  working  with  mental 
tests  cannot  afford  to  neglect.  Granted  a  degree  of  physical 
and  mental  correlation,  and  that  this  period  is  a  transitional 
one  for  physical  development,  then  the  whole  question  of 
qualification  for  school  entrance  is  thrown  open  anew.  The 
problem  is  still  further  complicated  by  the  fact  of  great 
variability  shown  in  the  developmental  factors  at  this  time. 

In  view  of  their  close  relationship  to  other  phases  of  physi- 
cal development,  and  in  the  absence  of  definite  methods  of 
grading,  the  question  arises  as  to  whether  the  time  of  ap- 
pearance of  the  first  molars  could  not  be  cited  as  a  point 
before  which  school  duties  should  not  be  imposed. 


314  PHYSIOLOGICAL  AGE   AND   SCHOOL   ENTRANCE 

The  differences  of  the  sexes  at  this  period  also  suggest 
some  important  problems.  Recalling  that  the  female  reaches 
maturity  some  three  years  earlier  than  the  male — or  nearly  so 
— and  that  she  reaches  the  pubescent  stage  almost  two  years 
earlier,  on  the  average,  the  fact  that  she  has  progressed  fur- 
ther at  the  school  entrance  age  is  to  be  expected.  The  ques- 
tion arises  here,  however,  as  to  how  early  the  differentiation 
of  the  sexes  actually  begins.  Since  differences  in  the  averages 
of  absolute  measurements  are  noticeable  at  birth,  and  in  view 
of  the  popular  opinion  that  the  prenatal  period  is  shorter  for 
females  than  for  males,  one  is  tempted  to  raise  the  question 
as  to  whether  differentiation  does  not  actually  begin  before 
birth. 

The  problem  of  the  amount  of  difference  between  the  sexes 
comes  up,  and  also  the  further  one  of  working  out  a  method 
sufficiently  refined  to  measure  them.  The  question  as  to 
what  this  difference  signifies  for  the  pedagogy  of  this  period 
of  life  is  an  extremely  important  one. 

The  preceding  facts  and  conclusions  form  the  basis  for 
some  further  conclusions  and  suggestions  for  the  hygiene  and 
pedagogy  of  the  early  years  of  childhood. 

We  have  shown  that  boys  and  girls  of  equal  age  are  not 
equally  advanced  physically  at  the  school  entrance  period  of 
life.  We  have  presented  a  mass  of  evidence  in  support  of 
the  conclusion  that  this  is  a  transitional  period  in  the  physical 
development,  referring  to  the  great  individual  variability,  as 
indicated  by  dentition,  skeletal  development,  etc.  Associat- 
ing these  facts  with  the  indications  of  a  correlation  between 
mental  and  physical  development,  the  need  of  a  physiologi- 
cal grading  for  entrance  to  school  becomes  strikingly  evident. 
Granted  a  proper  grading  for  entrance  on  this  basis,  the  grief 
and  the  expense  of  "  repeaters  "  up  through  the  grades  would 
be  tremendously  lessened.  School  entrance  should  be  on  the 
basis  of  the  fitness  of  the  individual,  not  on  the  basis  merely 
of  his  chronological  age. 

Again,  the  rapid  growth,  the  ease  with  which  the  delicate 
balance  of  the  organism  may  be  overthrown,  the  lasting  detri- 
mental results  following  the  wrong  "  inclination  of  the  twig," 
all  suggest  that  the  thing  of  supreme  importance  in  these 
early  years  is  rather  health  and  development  than  formal 
school  work.  The  paramount  importance  of  habits  of  health  is 
shown  over  and  over  again  in  case  of  the  teeth.  Lack  of  the 
habit  of  cleanliness  of  the  teeth  is  followed  by  caries,  loss 
of  bicuspids  or  all  important  first  molars,  with  probably  ill- 
fitting  permanent  dentures,  deformed  facial  features  and  in- 
jury to  health.  Habits  of  thumb-sucking,  mouth-breathing, 


PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE  315 

and  the  like,  may  cause  malocclusion  and  abnormal  growth 
of  jaws  and  related  facial  parts.  Good  permanent  tooth 
crowns  are  largely  dependent  upon  fresh  air,  exercise  and 
good  nourishment  throughout  the  first  five  or  six  years  of 
life.  Attention  to  all  these  things  should  be  first  until  after 
the  organization  of  the  childish  body  is  more  nearly  complete. 

The  eyes  are  unfit  for  close  visual  work  until  after  the 
transitional  period. 

Adenoids  left  uncared  for  in  these  early  years  are  liable 
to  cause  disturbances  of  development.  According  to  Yearsley 
(104)  the  time  to  have  them  removed  is  after  six  months 
and  before  six  years  of  age. 

Enlargements  of  the  tonsils,  with  decreased  power  to  resist 
invasions  of  micro-organisms,  accompanies  eruption  of  the 
first  molars,  in  many  cases  (100,  p.  13).  Until  after  this 
time,  no  child  should  be  confined  to  the  school  room  where 
his  chances  of  exposure  to  infectious  disease  germs  are  in- 
creased. 

In  view  of  all  these  things,  this  survey  would  be  worth 
while,  even  though  it  did  no  other  thing,  could  it  portray  in 
its  true  light  the  importance  of  all  the  years  of  earlier  child- 
hood for  the  normal,  healthy  physical  development  of  the 
child. 

From  a  different  viewpoint  another  suggestion  is  in  place. 
Could  "  types  "  be  agreed  upon  for  use  in  comparisons  of 
stature,  and  like  physical  characteristics,  similar  to  these  used 
in  anthropometry,  much  more  accurate  knowledge  of  develop- 
ment might  be  gained.  Grouping  of  material  according  to 
types,  combined  with  comparisons  of  relative  advancement, 
such  as  we  have  used  above,  should  lead  to  more  satisfactory 
results  in  indicating  stages  of  development. 


FINAL  SUMMARY. 

The  main  conclusions  to  which  the  facts  presented  in  this 
thesis  point  are: 

1.  That  there  is  a  mass  of  evidence  indicating  a  transition 
in  the  physical  development  of  the  child  at  the  period  of  usual 
school  entrance. 

2.  That  there  is  evidence  to  show  that  girls   are  on  the 
average  more  advanced  in  their  physical  development  at  this 
period. 

5.  That  requirements  for  entrance  to  school  based  on  stage 
of  progress  in  physiological  development,  or  physiological 
age,  would  be  far  superior  to  a  requirement  taking  account  of 
chronological  age  only. 


316  PHYSIOLOGICAL   AGE   AND   SCHOOL   ENTRANCE 

4.  That  in   the  application  of  physical  measurements   for 
the  purpose  of  finding  degree  of  progress  in  physical  develop- 
ment, a  method  indicating  the  percentage  of  adult  size  at- 
tained  at   a  given   age  is   superior  to   a  method   comparing 
absolute  data  directly. 

5.  That  the  hygiene  and  pedagogy  of  this  period  are  of 
prime   importance   for   the   future   development   and    welfare 
of  the  individual. 


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PHYSIOLOGICAL   AGE   AND   SCHOOL    ENTRANCE  321 

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